This website provides access to the wealth of MESSENGER mission news and data. Though accurate at the time of publication, it is no longer being updated. For the latest on Johns Hopkins APL space missions, visit
Resources / News Archives
Questions and Answers

From 2011 to 2016, the years encompassing MESSENGER's orbital exploration of Mercury and the archiving of all of the data from the mission with NASA's Planetary Data System, the mission's website featured a "Q&A" webpage. The Q&A page offered a way for people to submit a question to the MESSENGER science and engineering teams. During this time period, several hundred questions were received and answered. The questions and associated answers were placed into the nine broad categories shown below. Following the conclusion of the mission in 2016, the Q&A portion of the MESSENGER website was discontinued. The Q&A text below was captured as an archive of this effort, though some links contained in the archived text may no longer be preserved.

Questions about data from MESSENGER

Dear sir,I want to do my research work on Sun and Planetary systems using X-ray Spectroscopy.MESSENGER also contain X-ray Spectrometer in which it is having two detectors XRS (looking at Mercury, having 3 GPC detector) and SAX (looking at Sun, having Si PIN detector)I Could archive data for XRS (data from mercury) from the link below I couldn't archive data from SAX (data from Sun)Please suggest me the source from which I can get this data.Thank You - submitted by Harsh Pandit, Other educator, 11-13-2014

All of the MESSENGER XRS data records contain the spectra from the three gas proportional counters that look at Mercury and from the SAX Si-PIN that looks at the Sun. So you have already found the location of the SAX data. The reason they are combined is that we cannot analyze the spectra from the planet to determine surface composition without knowing the solar spectrum. The Sun is the source of the x-ray fluorescence that we detect from the planet. As you probably know the solar output can change on very short time scales, minutes and even seconds. So we need to measure the solar x-ray output continuously in order to analyze the planetary spectra.

The document that describes the contents of the XRS EDRs can be found at That will explain how to access all the information in each XRS data record, including the solar data.

Finally, you may be interested to know that several solar physicists have shown interest in our SAX data and have presented some analysis of SAX data at scientific conferences.

--Richard Starr, Catholic University
MESSENGER XRS Instrument Scientist

Why don't you include the depth of the craters and the height of cliffs and mountains? It would make the pictures more interesting. - submitted by Ray Gale, Interested public, 07-21-2014

It's great to know that readers of the MESSENGER web Gallery are hungry for more information! Each Gallery image caption includes the pixel dimension (in meters per pixel) and some indicator of the scale (for example, the width of the image in kilometers, or the length or diameter of some feature in the scene). The pixel dimension is automatically computed for each image based on the known field-of-view of the MDIS WAC or NAC camera optics and the slant distance from the spacecraft to the surface at the instant that the image was captured.
The vertical dimension of landforms in the images, such as the depth of a crater or the height of a cliff, cannot be determined automatically from a single image. In order to derive heights and depths, one must consult a topographic map constructed either from stereo image pairs or from measurements by the laser altimeter (MLA). Because of the spacing between the MLA tracks, MLA topographic profiles may not be available for some smaller features.
If the Sun is low enough that a feature casts a measurable shadow, then knowledge of the incidence angle can be used to compute the height of the feature that is casting the shadow. Shadow-length measurements are performed occasionally for specific features of interest, but this is not done routinely for every image.
Height and depth information certainly adds to the interest of an image. In the future, we will try to include heights and depths of prominent features in cases where the information can be quickly determined by consulting an existing topographic map.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

In the Gallery image from July 2, 2014, don't you mean 32.27 meters per pixel? 3227 m per pixel is more like taking photos of Jupiter at a great distance, like Voyager after Jupiter magnetosphere insertion. - submitted by Max Power, 07-03-2014

The July 2 image featured in the Gallery under the title "You Are Terminated!" does indeed have a resolution of 3227 m/pixel (3.2 km/pixel). The pixel scale of an image is dependent on the distance between the camera and the target area on the planet's surface, as well as the design of the camera's fore-optics that focus the light onto the CCD detector.

Here is a way to get a feel for the scale of this image: Mercury has a diameter of 4880 km. The MDIS CCDs are 1024 pixels square. Thus if Mercury exactly filled the field of view of an image, the pixel scale would be about 4880 km/1024 pixels = 4.8 km/pixel. The image featured in "You Are Terminated!" does not quite show Mercury's entire diameter, thus a resolution of 3227 m/pixel (3.227 km/pixel) is roughly in line with expectations.
Here are the specifics for this particular image. The MDIS Wide Angle Camera telescope gives a 10.5 x 10.5 degree field of view. The slant distance between MESSENGER and the target area on Mercury was 9028 km when the terminator images were taken. Thus, the distance across the whole image is [9028 km x (tangent of 10.5 deg)] = 1673 km. When this distance is divided by 1024 pixels, we see that the pixel scale is about 1.63 km/pixel. Now, why does this differ from the value of 3.23 km/pixel reported in the caption on the website? This image was obtained with the camera looking an oblique angle. In other words, it was not pointed straight down at the surface directly below the spacecraft. The reported pixel scale is that at the center of the image. In an oblique image like this one the pixel scale varies in the direction away from the edge of the image that is closest to the camera - increasing as the pixels toward the limb become more and more stretched out because of foreshortening.

For comparison, here is an image from the Narrow Angle Camera (NAC) with a resolution of about 30 meters/pixel. The distance between MESSENGER and Mercury was 1209 km when this higher-resolution image was captured. The NAC field of view is 1.5 x 1.5 degrees. Much more detail is visible when the resolution is increased by 100 times! 

Thanks for your question. It is good to have interested readers who prompt us to double-check our work.

--Ariel Deutsch (MESSENGER summer intern) and Dave Blewett (MESSENGER Participating Scientist),
Johns Hopkins University Applied Physics Laboratory

Dear Sir, I have downloaded your latest MLA data from release #11. In the available file you state that the lowest observed point is -5.8 km while the highest is 4.1 km. Further on in the same document you state that the topography values range from -6.2 km to 4.2 km. So, which is the actual range of elevation on Mercury? Also, I would like to know why the .jp2 files result to have wider ranges when put in ArcGIS (-11916 to 4967 for hdem_55n_500m.jp2, and -11620 to 8133 for hdem_64.jp2), is there a way to get the actual elevation in meters? Thank you!! - submitted by Valentina, Interested public, 03-10-2014

At one time, the lowest elevation determined by MLA was in Rachmaninoff crater at about -5.8 km, and the highest point was at 30.342°N, 116.93°E, 4.143 km. But since then we have been ranging obliquely into Prokofiev crater, in which there is a smaller, radar-bright crater (named "Z" in John Harmon's radar maps), whose depth is about -6.22 km, at about 85.4°N and 62.8°E. We have found some high spots above 4 km. I'm checking to see whether there are any higher than 4.143 or if those are mistakes. So far all data are under 4.2 km with respect to the 2440-km radius sphere.

--Greg Neumann, NASA Goddard Space Flight Center
MLA Instrument Scientist

JP2 does not support floating point data, so that the stored 16 bit values need to be properly scaled. Information on the scaling is provided in the associated label (.lbl) files. For example, ( gives a SCALING_FACTOR value of 0.5 and an OFFSET of 244000 to convert to meters.

--Kris Becker, U.S. Geological Survey

Dear Sir,I am interested to get access to the MLA data. I worked with the MOLA data to produce images from Mars in the last decade. I have now a contract to make a an image of the one of the Rupes on Mercury: Discovery Rupes, Victoria Rupes or Carnegie Rupes. It would be great to get access to the MESSENGER DEM data. I can also live with an unshaded digital elevation map or both to see what would give the best results. For results of images made with the MOLA data see: .Thanks and all the best,Space Artist Kees Veenenbos - submitted by Kees Veenenbos, Interested public, 01-16-2014

Image and DEM mosaics are available on the MESSENGER project website: ../Explore/Images.html#global-mosaics . You can also browse and overlay various image and DEM products with Mercury QuickMap:  QuickMap can produce 3-D perspective views.

MLA data in digital format can be obtained from the NASA Planetary Data System (PDS). MLA data reduced and gridded datasets are at

Note that Mercury Laser Altimeter (MLA) is only able to map in the northern hemisphere because of the highly elliptcal shape of MESSENGER's orbit. Discovery Rupes is in the southern hemisphere, but both Victoria and Carnegie Rupes are in the north.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How many pictures has MESSENGER offically taken since it started studying Mercury? - submitted by Nate Miller, High school student, 11-08-2013

As of today, Nov. 12, 2013, at 12:15 pm ET, MESSENGER has returned to Earth 197,035 images that were acquired by the cameras (MDIS, the Mercury Dual Imaging System) since the spacecraft entered orbit about Mercury in March, 2011. Before entering Mercury orbit, MESSENGER acquired 13,080 images; some of these early images were for calibration purposes, some were imaging that took place while the spacecraft was cruising to Mercury, and some were obtained during the spacecraft's three flybys of Mercury flybys prior to entering orbit. But overall, the vast majority of images have been collected since MESSENGER began orbiting Mercury. The mission is capable of lasting until early 2015, so we all look forward to many additional images to come!

--Nancy Chabot, Johns Hopkins University Applied Physics Laboratory
MDIS Instrument Scientist

Hello, I am interested in actual reflectivity (albedo) distribution of Mercury's surface. Apparently the global mosaics of Mercury (../Explore/Images.html#global-mosaics) at individual bands are useful, but do the values restored in each pixel represent reflectivity? Did you modify the actually observed values for display purpose (to enhance the contrast, for instance)? I know "Enhanced Color Mosaic" are enhanced in color, but how about "Global Mosaic in Color" at each individual bands? - submitted by Matilda, 10-10-2013

Any files in PNG format have been contrast stretched. That is, the physical units in the calibrated image have been scaled to the range 0-255 for storage in a PNG.

For the "Mosaics Using Images from NASA's PDS": both the PNG's and GeoTIFF's are contrast stretched from I/F (reflectance) units ~0.005-0.25 to 0-255 greyscale byte pixels.

For the physical unit versions, a global mosaic at high resolution would be very large, and a lot of TIFF reader software does not support floating point pixels. So the best option may be to use the individually mapped subregions at the NASA Planetary Data System (PDS).

Here are links to an introduction to the layout of the monochrome and color maps. ISIS may be a good choice for working with MDIS data also. A good intro is found here.

The files listed under "Download individual bands, 665 m/pixel geotiff files" ARE in floating point values of the calibrated physical units. The physical units for the color filter files are reflectance (I/F); the incidence, emission, and phase images are in degrees. As noted on the webpage, they are 32-bit floating point GeoTIFFs. Unfortunately, only a subset of software that support the TIFF format will read these floating point pixel versions correctly. The eight calibrated color filter images can be stacked into an image cube, and the color spectrum of each pixel can then be extracted. Other image processing techniques like color ratios or principal components analysis can also be applied to the eight-band cube.

--Chris Hash, Applied Coherent Technology Corp.
MESSENGER Science Operations Center

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Re: "Heine's Splash of Light" EW0244776297G.3band.mapped.PNG. Release date August 28, 2013I notice the red and blue dots which I understand may have to do with pixel anomalies. However, when I examine this image closely (especially evident in the top corner) there seems to be a reddish border tracing certain geographical ridge like features that gives the impression of some kind of radiance or energy release. Is this an image filter/color distortion, or is it an accurate color representation of the planet's surface? - submitted by James Watts, Interested public, 08-30-2013

In the image titled "Heine's Splash of Light" there are a few bad pixels (similar to the small cluster in this image, pointed out by another eagle-eyed reader). However, the overwhelming majority of pixels in the scene provide an accurate measure of differences in the reflectance properties of materials on the surface of Mercury. Keep in mind that the representation in the image is not what would be seen by the human eye. The color composite image is made by displaying images taken through three different color filters in the visible and near-infrared. The variations
in the image correspond to real differences in the ways that Mercury materials reflect light of different wavelengths (frequencies), however in absolute terms the color variations are
much more subtle than the human eye can perceive. In this composite (996, 748, 433 nm in red, green, and blue), areas that appear reddish do indeed reflect more light at longer ("redder") wavelengths than areas that have a bluish appearance. Note that according to Planck's law, all materials at temperatures above absolute zero emit electromagnetic radiation. Mercury's dayside surface is quite hot in relation to the surface of the Moon, for example. But Mercury does not get hot enough to have "radiance or energy release" at wavelengths in the visible or near-infrared (where the MDIS camera is sensitive).

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I presume the blue spot in this image is a photographic artifact? ../Explore/Science-Images-Database/pics/EW0252467201G.3band.mapped.png - submitted by Nigel lavery, Interested public, 08-06-2013

You have a keen eye. You are referring to a small blue spot that can be seen on the western rim of a degraded crater in the left middle of the August 7, 2013 gallery image. Your question prompted the MDIS team to evaluate the three-band image set used to make the color composite image shown in the gallery image. It turns out that there is a small cluster of bad pixels in the image taken through the 430-nm filter. Since this image is in the blue band in the color composite, the little cluster shines through as a blue speck. The cluster is probably the result of a solar energetic particle (SEP) or a cosmic ray that struck the CCD detector array as the image was being exposed. Small hits like the one in the Aug. 7 image, or in the image shown here, are not generally a problem. Occasionally, however, large numbers of SEPs can strike and seriously diminish the scientific usefulness of an image or set of images.

--John Kraemer, MESSENGER summer intern and Dave Blewett, MESSENGER Participating Scientist

i have 4.1.) what is some of the data collected from mercury from messenger?2.) how was data collected?3.) who do you think will use the data?4.) what boundaries did the engineers and scientist have to consider? reply as soon as possible - submitted by maxwell edwards, Middle school student, 05-21-2013

You may like to browse the MESSENGER website, which contains a wealth of information including material on all the questions you have asked. In particular,

1 and 2: The data are collected by MESSENGER's science instruments. You can read about the operation of these instruments and the data they obtain here.
All of the data are available through NASA's Planetary Data System. The datasets are collected in order to answer specific questions about Mercury.

3. The initial users of the data are the members of the Science Team. Once datasets are delivered (about every six months) to the NASA Planetary Data System, it is freely available to scientists and the public from around the world. You can see a listing of all the scientific papers that have been published by MESSENGER team members here.

4. A summary of the challenges of designing a spacecraft to orbit Mercury is given here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Dear Sir/Madam, I am working with MESSENGER radio science raw data (Orbit Determination Files (ODF)), in order to simulate the MESSENGER orbit. But i need little data to proceed: 1. Where i can find latest spherical harmonic coefficients (Cnm and Snm ) of the Mercury gravity field? Is there any publication by your teams about this gravity field model? 2. Where i can find the information about the maneuvers, such as maneuvers timing, mass flow rate, thrust .. etc? I have found related file in pdsgeoscience website, which is called maneuvers dump momentum (mdm). Now i need to ask, is it the complete information about the maneuvers or do we have some other source also for this informations?Thanks in advance.

- submitted by Ashok Verma, College student, 10-20-2012

1. The latest published coefficients for the gravity field are in Gravity Field and Internal Structure of Mercury from MESSENGER, David E. Smith et al., Science 336, 214 (2012); DOI: 10.1126/science.1218809.

We archive all the publicly available data at the Planetary Data System (PDS), in the geophysics node, and you will find additional, higher-order coefficients there, once they are released in March 2013. Those data will be part of the Radio Science (RS) Reduced Data Records (RDRs). You can find the MESSENGER RS data at   All the latest data will be archived there. You can also find the schedule for future releases of data at the PDS.

2. The RS PDS archive also contains the raw data (Doppler measurements or ODFs) and most data that are required to analyze those raw data. That includes data on the maneuvers, which you have found. There are also Small Forces Files (SFFs), but the momentum-dump maneuver (MDM) file contains all the maneuver information that you should need for your analyses. Normal operations during orbit includes only one commanded momentum dump every two weeks or so. There are no autonomous momentum dumps, and the MDM file includes all the orbit correction maneuvers (OCMs), too.

The other auxiliary information that you will need are the antenna-configuration (ant) files. They enable correction for Doppler shifts due to changes in attitude. If you have not checked, yet, the Software Interface Specification (SIS) contains lots of useful information. If you find something missing, you can send us an email and we will fix it in the next version.

--Mark Perry, Johns Hopkins University Applied Physics Laboratory
MESSENGER Geophysics Discipline Group

First, let me thank you for providing the data, pictures and state-of-the-research artistic impressions on this webpage. As a science fiction writer devoted to scientifically accurate scenarios, I really appreciate sources like this. Now, I have a question concerning maps of mercury. There are plenty of mosaic images of the mercury surface available in the web, but none of them are in any way labeled. I also tried the Google Earth feature with messenger data, but it only runs very buggy on my system. So, is there a simple, labeled map of the Mercury surface available as a graphic file? Also, I would be grateful for a map showing the distribution of peak and average temperatures on Mercury. When I read about the "cooler meridians" caused by the 3:2 resonance between rotation and orbit, I was thrilled by the possibility of regions on Mercury where it could be possible to establish subterranean stations or even permanent colonies with habitable temperatures. - submitted by Markus Gerwinski, 10-02-2012

We're glad that MESSENGER's bounty of data is inspiring to artists as well as scientists. The mosaic you are looking for is available on the MESSENGER project website. Look along
the left edge for the box named "Explore Orbital Data with Quickmap". Using Quickmap, you can display global mosaics, overlay latitude/longitude lines, locations of named features, and so forth. Enjoy!
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hello...I would first like to say that I think I really like this particular web site. I would go into details in the future. I believe on the first web page or the home page on the web site that there should be an 'image button' where you would get a simple, comprehensive, database of messenger spacecraft images to peruse. I am finding it very hard to locate that section of the web site. Am I doing something wrong..will this web site change in order to clear up this deficiency? Thanks for any and all responses. Bye, Peter - submitted by Peter, Interested public, 05-05-2012

All MESSENGER data are made available to the public through the NASA Planetary Data System approximately every six months. You can begin your image search here:

The MESSENGER public website does offer interactive mosaics, through the QuickMap interface:

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hi I get these low-level updates but is there any science data site, please? I can look in Icarus , Ap J and Nature but not most other journals (retired - no university or "corporate" library access).  Thanks. Peter Noerdlinger - entered by Q&A admin, 04-17-2012

There is a wealth of information available on the MESSENGER web page. For example: the publications page has links to papers in the peer-reviewed literature. The presentations page has links to the major scientific and engineering conferences where MESSENGER results have been presented (most of the abstracts are available to anyone - no subscription or fees involved). The MESSENGER image gallery releases new images, mostly from the camera, five days per week. You can browse global mosaics from the various imaging campaigns using Quickmap. All datasets from NASA planetary spacecraft are archived in the Planetary Data System; MESSENGER data are here.

--David Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hello MESSENGER! My question is in regard to the photo titled "Easy as 1-2-3!" I noticed two red dots in the upper-center of the image. One is located about at the crater edge. What are these? I've worked as a NIMA photointerpreter before, and I'm an amateur photographer. I have also performed a lot of free photointerpretation for the Mars HIRISE stuff back early in the 2000's. *Anyway,* I *assume* that the dots are due to lens flaws, maybe CRI's? I'd rather it be something more interesting. Will more of these 'dots' show up? Thank you! I wouldn't have been able to sleep tonight ;-) if I hadn't sent this query.  - submitted by bruce tabor, Interested public, 04-13-2012

In general, there are several possible reasons for a "red spot" to appear in a color composite MDIS image like the one you mention. First, there are real color variations on the surface, related to the composition of the rocks, that can cause an area to appear red. Second, there could be a problem with registration of the individual images that are used to make the color image. Recall that MDIS takes images successively through colored filters (pieces of glass with special coatings so that they transmit only a narrow range of wavelengths). Since the spacecraft is moving, each image in a color sequence does not cover the exact same patch of ground on Mercury's surface. We use image processing algorithms to mathematically shift each image so that the same point of ground is in the same pixel position (row and column) in the entire stack of images in the image cube. A slight misalignment could cause a spurious color feature to appear. Third, solar energetic particles or cosmic rays could hit the MDIS CCD, causing a "hot pixel." During a solar storm in March 2012, a number of MDIS images were affected by this problem. I looked closely at the MDIS 1000-nm image used to make the color composite to which you refer. The 1000-nm image was displayed in the red channel, so a hot pixel in that image could cause a red spot. I found three pixels in this image that have unusually high values compared to the surrounding pixels. One of the pixels is in the shadowed portion of a small degraded crater, and the other two are next to each other on the rim of the large crater Sholem Aleichem, again mostly in shadow. So these anomalous pixels are the cause of the red spots that you see. I suspect that they were caused by cosmic ray or solar particle hits. If it happened to be the 750-nm filter that was affected, then you would have seen green spots.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Re: image # 1207843 acquired December 31, 2011 and displayed in the "Gallery" as "View of a Scarp". In this image there are faint lighter parallel and evenly distirbuted striations running generally top to bottom across the entire width of this image. At first I thought it was just a grainy distortion in the image, but on closer examination it is apparently on the surface of the planet. What would cause this kind of fine texturing of the surface? - submitted by James Watts, Interested public, 01-11-2012

One of the challenges of operating MDIS in orbit about Mercury is balancing how many images are acquired, and hence how much of the surface is seen, at any given time with the limitations of storing the acquired images on the spacecraft's solid state recorder and the availability of resources to downlink those images to Earth. One of the ways available to MDIS to achieve this balance is to slightly compress the images on the spacecraft once the images are acquired but before they are downlinked to Earth. This makes each image a bit smaller and enables a larger number of total images to be acquired. In the featured image that you refer to, what you are noticing are minor artifacts introduced by the compression algorithm applied to the image onboard the spacecraft.

--Nancy Chabot, Johns Hopkins University Applied Physics Laboratory
MESSENGER MDIS Instrument Scientist

Hello,  Where can i find the statistics about how much data (images or bytes ) MESSENGER produced by the MDIS system. - submitted by Fabio Andrijauskas, Other educator, 10-05-2011

There is no publicly available counter that is registering the volume of data returned by MDIS or other MESSENGER instruments. As of October 5, 2011, MDIS has collected 54,568 images during orbital operations. MESSENGER data, when released, is available to anyone through the NASA Planetary Data System.

--Nori Laslo, Johns Hopkins University Applied Physics Laboratory

MDIS Mission Operations Lead

I would very much like to see the radar data as a greyscale image with white as high altitudes and black as the lowest in the detail available. There are many free and otherwise programs that could take that and allow one to "look around" and see what those landscapes would look like from various views. Matching the greyscale with photographic view would make that super awesome. - submitted by Bob Danforth, Interested public, 06-18-2011

MESSENGER does not carry a radar instrument, so I'm guessing you actually mean data from the laser altimeter (sometimes called a "lidar"). (Note that Earth-based radar has been used to make images of Mercury's surface.) You can see a movie of the laser altimeter (MLA) coverage here. Topographic data from MLA can indeed be processed into a map or image. It is also possible to "drape" images from the camera over the topographic model to provide perspective views. Data products of this type will be made as the mission progresses.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hi, I wonder if all of Mercury's surface has now been covered in photos (hi- or lowres.)? If so, when did this happened? If not, will it happen - or when? Regards, Daniel Tingdahl, Sweden - submitted by Daniel Tingdahl, K-12 teacher, 05-15-2011

After MESSENGER's three Mercury flybys, the areas of Mercury's surface that remained unseen (by either Mariner 10 or MESSENGER) were at the north and south polar regions. After the mission completes one Mercury solar day in orbit (176 Earth days), the entire surface near the south pole will have been imaged. However, there will still be a small region near Mercury's north pole that will not have been covered by spacecraft imagery.

MESSENGER's highly elliptical orbit brings the spacecraft far above Mercury's south pole and low over Mercury's north polar region. Thus, the south polar region can be seen with just a few images while the image footprints in the north polar region are much smaller and many more images are required to cover the entire surface. Also, the orbit is not perfectly north-south but has an inclination currently of 82.5°. Thus the spacecraft does not pass directly over Mercury's north pole and to image that portion of the surface can be disruptive to the operations of other instruments. After the first Mercury solar day in orbit, a global base map of Mercury's surface will have been built up and areas that remain unseen will be the focus of special targeted images, including this region near Mercury's north pole. Overall, by the end of the year-long mission, we hope to have imaged all of Mercury's surface, including the most challenging area near Mercury's north pole.

--Nancy Chabot, Johns Hopkins University Applied Physics Laboratory
MESSENGER MDIS Instrument Scientist

Will the Gamma Ray Spectrometer yield oxygen isotope ratios? - submitted by Chandler Kennedy, Interested public, 04-27-2011

The MESSENGER gamma-ray spectrometer (GRS) is sensitive to individual nuclear isotopes, so in principle isotopic ratio measurements are possible.

In the case of measuring oxygen isotopic ratios, such a measurement is difficult because of the expected isotopic enrichment. On Earth and the Moon, oxygen isotopes are found with the following abundances: Oxygen-16 (99.762%), Oxygen-17 (0.038%), and Oxygen-18 (0.200%). As you can see, only a small fraction of oxygen is found for isotopes other than Oxygen-16, and these abundances are below the measurement sensitivity of the GRS.

A better example is Mg, where the isotopic enrichments are: Magnesium-24 (78.99%), Mangesium-25 (10.00%), and Magnesium-26 (11.01%). Each of these isotopes also have measurable gamma-ray fluxes, therefore an isotopic measurement of Magnesium is potentially within the detection capability of the GRS. Unfortunately, the GRS housing contains substantial amounts of Magnesium, so effort will need to be made in understanding the background signals before Mg isotope measurements could be announced.

--Patrick Peplowski, Johns Hopkins University Applied Physics Laboratory

MESSENGER Geochemistry Group


Can MESSENGER get information on isotope ratios of Ca and Mg emitted by Mercury? - submitted by Chandler Kennedy, Interested public, 04-22-2011

The MASCS instrument will make observations of the abundances of Ca and Mg in Mercury's tenuous atmosphere (a surface-bounded exosphere). However, it will not get isotope information. The spectral lines are too close together for MASCS to resolve. Also, there would also have to be a significant amount of the less-abundant isotope compared to the normal one for us to even have a chance at seeing a line from it, and this is unlikely given the low densities in Mercury's exosphere.

--Ron Vervack, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

First my congratulations for a wonderful job placing the probe where it is. As I am a hobbyist who likes to explain to the German people about MESSENGER and the Mission. I like to display the current position.

Obviously the SPICE kernels NAIF makes accessible for the public are not displaying the actual state of the mission. It would be great if you can assist me by sending me an actual spacecraft kernel or a link where to get it. Thomas Wehr - entered by Q&A admin, 04-22-2011

The project is in the midst of discussions concerning official public releases of the SPICE kernels. However, the US Geological Survey's ISIS image processing software includes MESSENGER SPICE in its installation. The kernels are updated frequently.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hi Are you going to release 3D photos of Mercuty ? ; If so , when and in which format ?    Regards, Abraham Shpitz - entered by Q&A admin, 04-22-2011

Stereo anaglyphs have been prepared for several areas that were viewed at different angles by MESSENGER's camera during the Mercury flybys. Our image Gallery has one for the Rembrandt basin, and one showing a huge cliff cutting the crater Sveinsdóttir.

One of MESSENGER's goals is to create stereo views of Mercury's surface with an average resolution of 250 meters/pixel (820 feet/pixel) or better. During MESSENGER's one-year mission, the first set of views is acquired during the first 176 Earth days, and the second 176 days are used to acquire the complementary stereo base map. The stereo coverage will be used to produce topographic maps, and can also be processed for 3-D anaglyphs.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I have noticed that on just about all of the images returned from the MDIS-NAC camera some apparent degradation in image quality. Is there some ongoing issue with calibration or with focusing on this imaging system? For a modern CCD imaging sensor, there seems to be more degradation in image quality than one would expect. Thanks, Robert M. Elowitz - entered by Q&A admin, 04-21-2011

There is always a compromise between data quality and data volume. In order to map the entire planet, lossy compression is sometimes used to reduce the size of the data files that must be returned from the spacecraft. In some cases, NAC images for small targeted areas have been returned without compression. And of course, a manual contrast stretch has been applied to the images posted to our Gallery. The stretch may cause certain areas of the image to appear to be underexposed or saturated.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist
Mark Robinson, Arizona State University
MESSENGER Co-Investigator

Can you not post all raw images like Cassini and Mars Rovers? Stephen G., Kelowna, BC
Like your Opportunity and Cassini counterparts it would be nice to put all raw pictures taken by MESSENGER sorted by days. Pierre A. in Montreal.

- entered by Q&A admin, 04-08-2011

Some missions quickly make all raw data available on the web; others make selected releases of individual images accompanied by extensive discussion of the data. MESSENGER is a low-cost mission and, unlike the Cassini or Mars Rover projects, has only limited personnel available to validate images and other data. The process of collecting images with a spacecraft instrument, storing and compressing the data onboard, transmitting it to Earth, receiving the data, and archiving the information is a complicated process, and occasionally mistakes occur. For example, an image header could contain incorrect information about the size of the image. This error would cause the image to appear garbled and could lead someone unfamiliar with the data to assume that there was a problem with the camera. NASA requires that all raw and calibrated data from its missions be made available to the global public through NASA's Planetary Data System (PDS) website. MESSENGER data from the cruise phase (including the six planetary flybys) are presently in the PDS. Data from the orbital phase will be delivered to the PDS every six months. This six-month time cadence gives the team the opportunity to make careful checks to insure the integrity of the data before archiving and widespread dissemination.

--David Blewett, Johns Hopkins University Applied Physics Laboratory, MESSENGER Participating Scientist

--Sean Solomon, Carnegie Institution of Washington, MESSENGER Principal Investigator

Are your images based on raw data? Or do you do touch up work to the images before releasing them to the public? - submitted by Atom Charles, Interested public, 04-06-2011

The images released in our Gallery have undergone the standard MDIS calibration procedure. This involves the following steps:

a) On the spacecraft, the 12-bit pixel data values are converted to 8 bits for transmission to Earth. This is done with a look-up table. Once on the ground, the first step in calibration is to restore the 12-bit values with the inverse look-up table.

b) A linearity adjustment is applied to correct a small nonlinearity in the detector response.

c) The pixel-dependent dark level is subtracted; this includes the temperature dependence of the dark current.

d) Scene-dependent frame transfer smear for each pixel is subtracted.

e) The image is divided by the "flat-field" for the particular filter. This compensates for non-uniformity in the response of the pixels of the focal plane array detector and for possible blemishes on the filter.

f) The pixel values are normalized by dividing by the integration (exposure) time in milliseconds.

g) The image is divided by a responsivity function that relates the result of (f) to radiance. The responsively is temperature-dependent.

The result of this chain is to convert the camera's raw digital number (DN) values to physical units of the intensity of light striking the camera's CCD detector (radiance, watts per square meter per unit solid angle) in each filter bandpass.

The team uses the Integrated Software for Imagers and Spectrometers (ISIS), developed by the U.S. Geological Survey's Astrogeology Team (Flagstaff, Ariz.) for calibrating and mosaicking the MDIS images.

Finally, in order to display an image on a computer screen or to save it in a standard image file format (like JPEG or PNG), a contrast stretch is applied. This procedure maps the pixel radiance values to the 255 grey levels of the display.

All raw and calibrated data from all MESSENGER instruments will be archived in NASA's Planetary Data System (PDS). The data from the first three Mercury flybys is already there. Data from orbit will be delivered to the PDS every six months.

--Brett Denevi and David Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Geology Discipline Group

Topics related to the spacecraft hardware and challenges of operating in orbit around Mercury

What is MESSENGER made of so that it doesn't melt or burn up? - submitted by Maggie, Middle school student, 09-02-2015

The intensity of light from the Sun is about 10 to 11 times greater at Mercury than it is at Earth's distance. Therefore, in order for a spacecraft to operate successfully in orbit around Mercury, it must have a design that can handle the extreme thermal environment. MESSENGER's main defense against the Sun's heat was a sunshade made of ceramic cloth. You can read more about MESSENGER's thermal design at this link, which also shows a picture of the sunshade.

And you can read about other aspects of the spacecraft's design (including thermal) in the "Spacecraft & Engineering" section of the MESSENGER Q&A page.

Note that the spacecraft cannot "burn up" in the conventional sense of "being consumed by flames or fire". Fire requires oxygen, which is plentiful in Earth's atmosphere, but is not present in the vacuum of space.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Who (company) helped create MESSENGER? - submitted by Chris Franklin, Elementary school student, 05-18-2015

The MESSENGER spacecraft was built and operated by the Johns Hopkins University Applied Physics Lab in Maryland. A wide variety of other organizations (including NASA centers, universities, and private companies) contributed to the mission by supplying components, instruments or services.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

what problems did messenger encounter? - submitted by vannsa, Middle school student, 03-20-2015

That is rather a broad question. There are numerous challenges involved in operation of a spacecraft around the planet closest to the Sun. The spacecraft was designed to meet these challenges; you can read about the design here. The spacecraft has occasionally been blasted by energetic particles from solar storms, causing interruption of data collection by some instruments. You can see the effects of a solar storm on the images obtained by the camera here. When the spacecraft first entered Mercury orbit and experienced higher temperatures, an outgassing episode affected the filters of the Wide-Angle Camera, complicating calibration. The steps involved in this calibration were described in an abstract by Mary Keller and colleagues presented at the 2013 Lunar and Planetary Science Conference. Other "problems" relate to expected degradation in performance of systems, for example, the power output of the solar photovoltaics has declined slowly but steadily (and in accordance with predictions) over the years of the mission. The cooler for the Gamma Ray Spectrometer (GRS) ceased functioning, but it was known to be a limited-lifetime component. And the GRS has since been repurposed as a neutron detector that complements the measurements made by the Neutron Spectrometer. The biggest "problem" is that the fuel for propulsion has been nearly exhausted. Following a final series of maneuvers to boost the altitude of closest approach, gravity will take over leading to collision of the spacecraft with the surface near the end of April, 2015.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Good Afternoon to all at the MESSENGER team. I love the recently published super high resolution images from the MDIS NAC. Some of my favourites from that category are the gallery images from May 1, May 2, May 5, and May 8, 2014. Regarding the image EN1037173522M, 5 metres resolution, I see it was mentioned that the image is a little 'noisier' than most others, due to such a short exposure, and a very slight granularity is seen when blown up to full size, however, everything is still there, all the detail, the feaures including the newer craters are sharp and the ancient degraded ghost craters are still there, I suspect that 4 metre and even 3 metre resolution images are still possible, with out significant blurring, the MDIS is a very capable system. Truly, yours Andrew R Brown, Ashford, Kent, United Kingdom. - submitted by Andrew R Brown, Interested public, 05-29-2014

Images with pixel sizes of 5 m are really exciting, no matter whether you spell it "meter" or "metre"!

When devising the imaging plan for the low-altitude portion of MESSENGER's mission (less than about 350 km altitude), the science team is continually debating the trade-offs between high spatial resolution and image quality. When the spacecraft is passing low over the surface, it is moving extremely fast. Therefore, very short exposure times are needed to prevent image smear. In order to have minimal smear, the camera field of view must move across the ground less than the size of one pixel during the exposure. But very short exposure times necessarily mean that less light is collected by the detector, and hence the signal is lower. Lower signal translates to a lower "signal-to-noise" ratio, or a noisier image. One compromise is to "bin" the images. In other words, each 2x2 group of pixels in the original image is combined to form a single pixel in the resulting binned image. This reduces the pixel dimension by a factor of two (a 6 m/pixel image becomes 12 m/pixel), but boosts the signal in each binned pixel by about a factor of four over an unbinned pixel, reducing graininess. The phrase "To Bin or Not To Bin" is often heard at MDIS planning meetings.
Another concern related to low altitude operations is the temperature of the various spacecraft systems. Passing close to the hot surface of Mercury causes temperatures to rise. The dark-current noise of CCD detectors, like that used by the MDIS cameras, increases with temperature. The design of MDIS includes a clever "wax-pack" system to absorb heat and channel it so that it can be radiated away to space. Spending more time close to the planet means less time for the camera to cool down.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I am always interested in the design features of MESSENGER's systems. Particularly the masses of individual items like the sunshade or the solar panels. Where could someone go to get this kind of information? Is there a technical information source for exploration spacecraft available for historical referencing? - submitted by Bryce Johnson, Journalist, 04-17-2014

Descriptions of many of MESSENGER's scientific instruments were presented in a series of papers in the journal Space Science Reviews (volume 131) in 2007. Links to all MESSENGER-related publications can be found on the project's Publications webpage - you can peruse that listing to find papers of interest. In particular, a paper by A.G. Santo and colleagues provides information on the mass of the various spacecraft subsystems.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What does MESSENGER run on? solar power, fuel, or battery. - submitted by Simon, Elementary school student, 03-25-2014

Like most spacecraft that operate in the inner Solar System, MESSENGER gets its power from solar panels. A battery stores electrical power for the short occasions when the spacecraft is in eclipse (that is, passes into Mercury's shadow). Missions that travel to the outer Solar System, where the intensity of sunlight is too weak for solar panels to be practical, obtain power from heat generated by the radioactive decay of plutonium in devices known as radioisotope thermoelectric generators (RTGs). Spacecraft with RTGs include Voyager, Galileo, Cassini, and the Mars Science Laboratory (Curiosity).

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I'd like to be explained to about the propulsion systems and thermal design of the messenger spacecraft. It would be an honor to be informed on this revolutionary topic. Please, be a gentleman, and do me the greatest favor of replying. - submitted by Brian, Middle school student, 03-14-2014

Brief summaries of the spacecraft thermal design and propulsion system can be found on the MESSENGER project web page. The Publications listing on the website has a bibliography and links to published papers on all aspects of the spacecraft's engineering, including the propulsion and thermal control systems. A few that you may find to be of interest:

Ercol, C. J., and colleagues, Return to Mercury: An overview of the MESSENGER spacecraft thermal control design and update on orbital flight performance, Thermal and Fluids Analysis Workshop, paper TFAWS2012-PT-03, 26 pp., Pasadena, CA, August 13-17, 2012.

Ord, K. J., and K. E. Hibbard, MESSENGER power and thermal systems operations, SpaceOps 2010 Conference, American Institute of Aeronautics and Astronautics, paper AIAA 2010-2137, 10 pp., Huntsville, AL, April 25-30, 2010.

Wilson, M. N., and colleagues, Flight performance of the MESSENGER propulsion system from launch to orbit insertion, 48th Joint Propulsion Conference, American Institute of Aeronautics and Astronautics/American Society of Mechanical Engineers/Society of Automotive Engineers/American Society for Engineering Education, paper AIAA 2012-4333, 23 pp., Atlanta, GA, July 30 – August 1, 2012.

Wiley, S., and colleagues, MESSENGER propulsion system flight performance, 42nd Joint Propulsion Conference, American Institute of Aeronautics and Astronautics/American Society of Mechanical Engineers/Society of Automotive Engineers/American Society for Engineering Education, paper AIAA 2006-4389, 14 pp., Sacramento, CA, July 9-12, 2006.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How can the MESSENGER spacecraft resist the huge ammount of solar radiation? - submitted by Gabriel, College student, 03-09-2014

Great question. See this previous Q&A.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I am currently doing a MS Thesis on space-based LIDAR and was curious, to date, how many pulses does the MLA have on it? Is it still operating? Thank you!-John - submitted by John DeMello, College student, 11-04-2013

As of Nov. 5, 2013 the Mercury Laser Altimeter (MLA) is in operation. Its power has declined after years of working in an extreme thermal environment, but it is still acquiring topographic measurements of Mercury's northern hemisphere. The number of laser shots by Sept. 16, 2013 was 26,716,501. From these, 15,520,397 validated planetary radii were measured.

--Carolyn Ernst, Johns Hopkins University Applied Physics Laboratory
MLA Deputy Instrument Scientist

Are the photovoltaic cells on MESSENGER degrading at the expected rate? Is there an estimate available for how long these cells will continue to deliver adequate power? Thanks! - submitted by Bryce Johnson, Journalist, 02-28-2013

The engineering team occasionally performs tests to determine the efficiency of the solar power arrays. Fortunately, the results show that the power is declining at a slow but steady rate. It is not anticipated that there will be any serious limitations on power during a possible second Extended Mission.

--Dave Blewett
Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What is the temperature of the outside of the spacecraft? - submitted by Tim Jago, 02-22-2013

The outer surface of the sunshade gets up in the 650K (380°C) range when closest to the Sun. In eclipse or when facing deep space the outer surface of the Multi-Layer Insulation (MLI) drops down to extremely cold temperature below 100K (-173°C). Fortunately these insulate the main body of the spacecraft from the extreme environments and allow critical components in the main body of the spacecraft to stay comfortable at around room temperature (22°C) for the entire mission. 

--Shawn Begley, Johns Hopkins University Applied Physics Laboratory
MESSENGER Thermal Engineering Team

Hi, Is that possible to get some information regarding the transponder delay of the MESSENGER spacecraft during its orbital period ? I am particularly interested in computing the MESSENGER spacecraft orbit. However, in my computation i am getting some constant bias in the range. I believe it might come from the information which i have missed ! Could you please help me in this regard ? Thanks - submitted by Ashok Verma, College student, 01-29-2013

The short answer is 1371 nanoseconds. This is the averaged spacecraft delay for all MESSENGER antenna paths. The range could be as high as ± 20 ns (corresponding to a delta of 3 meters). A good reference for this data is Section 3 of this paper:
Srinivasan, D. K., M. E. Perry, K. B. Fielhauer, D. E. Smith, and M. T. Zuber (2007), Application of the MESSENGER radio frequency subsystem to meet the mission radio science objectives, Space Science Reviews, 131, 557-571.

The way MESSENGER has operated since entering orbit around Mercury has depended fully upon the Phased Array antennas while providing Ranging data. However, that would alternate between the Front and Back sides depending upon the phase of the orbits. Expect the Front Phased Array path to offer 1360 ns and the Back Based Array path to offer 1356 ns. These data were taken when the spacecraft was at room temperature, so the flight results will vary somewhat from these numbers. But hopefully differences in this order of magnitude are beyond the scope of the original question.

--Darryl Royster and Dipak Srinivasan, Johns Hopkins University Applied Physics Laboratory
MESSENGER Communications/RF Engineering Team

What kind of experiments did you do before hand? I'm doing a research paper on it, and I can't find anything on what experiments you did before hand. All I can do right now is summarize what the scientific instruments do. I'm interested in the GRS and the MLA. If you could reply quickly, that would appreciated. - submitted by Kellie Hunter, Interested public, 11-15-2012

I'm not sure what you mean by "experiments done before hand". The GRS (Gamma-Ray Spectrometer) uses well-understood principles of physics to detect gamma rays emitted by naturally occurring radioactive isotopes, as well as by radioactive species created by nuclear reactions produced by cosmic rays. The gamma-ray spectra that the instrument measures allow the elemental composition of the planet's surface to be determined. Gamma-ray spectrometers have been used on other planetary spacecraft (including Apollo 15 & 16, Lunar Prospector, Kaguya, Near-Earth Asteroid Rendezvous, Mars Odyssey).

Similarly, the MLA (Mercury Laser Altimeter) uses knowledge of the speed of light and the spacecraft's position to measure the elevation of the surface. Laser altimetry has also been widely applied to measure the shape and topography of planetary bodies. Laser altimeters were carried by missions including Apollo 15, 16, & 17, Clementine, Kaguya, Near-Earth Asteroid Rendezvous, and Mars Global Surveyor. Laser altimeters have also flown on Earth-orbital satellites, and are used for mapping from aircraft.

All the instruments underwent pre-flight calibration, as well as "shake and bake" vibration and thermal testing to insure that they are able to survive the rigors of launch and the environment in space on the way to and at Mercury.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Now that the science principal objectives of the mission were achieved, could new ones be created or put in the "first list of the queue"? I'm talking about communications: Mercury orbits the Sun in 88 days, so, we have many possible positions to emit and receive signals. Has MESSENGER any device who save the time when received and emitted a signal and transmit that numbers to Earth? Could we compare that values with the similar data produced in Earth? Because MESSENGER is a spacecraft so close to the sun is the ideal machine to learn about the effect of Sun, Mercury and Earth in signal transmission. Could this be reached? - submitted by Sergio Silva, Interested public, 08-09-2012

Throughout its mission, the MESSENGER spacecraft is in routine communication with Earth through NASA's Deep Space Network (DSN) ground stations (located in Goldstone (Calif., USA), Madrid (Spain), and Canberra (Australia)). Commands are uploaded to the spacecraft and science and engineering data are broadcast from the spacecraft to the DSN. Command
uploads take place twice per week. Data are received from the spacecraft every day during DSN contacts that last up to about 5 hours. (The exceptions are conjunction periods when
the Mercury-Sun-Earth angle is less than about 3 degrees.) The physics of interplanetary radio communication is well understood; this is what allows the spacecraft's radio system to be designed and the schedule of up- and downlinks to be routinely planned. Relativistic effects are incorporated into the timing of the radio signals.
-Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How did the amount of data collected during the primary mission compare with what was planned? What would have been the disposition of the MESSENGER spacecraft had the mission not been extended? Thanks for a great mission so far and good luck for the extended mission! - submitted by Craig Montero, Interested public, 04-05-2012

Here's an answer to the second part of your question. [We'll get to the first part when we can.]

Following Mercury Orbit Insertion (MOI) in March 2011, the disposition has always been that the spacecraft will impact the planet; there are no planetary protection issues for Mercury involved either nationally or internationally and the impact will happen as a result of orbital mechanics. Spacecraft orbits around Mercury are typically unstable due to the perturbations by the Sun's gravitational field. Following MOI there was insufficient propellant left in the spacecraft tanks to leave orbit. We do have enough propellant to control when – and, to some extent, where – the final impact point will be, but this will depend on the details of propellant usage in the next month, as we go to an orbit with a nominal 8-hour period. In any case, the best current projection is that MESSENGER will crash on Mercury (at several km/s) prior to mid-2015. You may like to browse other related questions in the Q&A Orbiting Mercury topic.

--Ralph McNutt, Johns Hopkins University Applied Physics Laboratory
MESSENGER Project Scientist

How did the MESSENGER spacecraft survive the X5.6 flare/CME two weeks ago? At the time Mercury took a direct hit from that event!  Thanks, John D. Patterson - submitted by John D. Patterson, Interested public, 03-27-2012

We're happy to see concern for MESSENGER's well-being from members of the public. Here's a response to a similar question.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How is MESSENGER bearing up during the recent 'solar storm'? Have there been any problems with the spacecraft from this event?  - submitted by Bryce Johnson, Journalist, 03-09-2012

The spacecraft is weathering the storm very well. There were a few temporary memory errors due to radiation-induced bit-flips, but on-board safeguard systems took appropriate action and the few affected units were successfully reset and resumed normal operations. One subsystem and one instrument were impacted in this way. Two other instruments whose detectors are sensitive to radiation took automatic action to protect the sensors and resumed normal operation after the storm passed. Spacecraft operations and science observations from all other instruments continued safely and were uninterrupted through the storm.

An example of the effects of the charged-particle bombardment on images obtained with MESSENGER's camera can be seen here.

--Brian Anderson, Johns Hopkins University Applied Physics Laboratory
MESSENGER Deputy Project Scientist

Hi I was wondering where you could find schematics of the MASCS and MAG on this mission as well as their data rates ?? - submitted by Jeremy Stone, College student, 03-01-2012

A comprehensive set of papers covering the full mission, spacecraft, and all of the instruments has been published in Space Science Reviews, vol 131, issues 1 to 3, 2007. This was republished as the MESSENGER Mission to Mercury book by Springer, ISBN-978-0-387-77211-0. It includes a 40-page paper on the details of MASCS (W. E. McClintock et al.) and and a 33-page paper on the details of MAG (by B. J. Anderson et al.). Refer to the MESSENGER Publications Page for more information on these papers.

-Rob Gold, Johns Hopkins University Applied Physics Laboratory
MESSENGER Science Payload Manager

Sir, I read with interest the Feb 3 MESSENGER News release, relating to the SciBox application. With so much work put into the software, and it's apparent flexibility, I was wondering if this tool is readily adaptable to other spacecraft? For example, could this same tool be used for New Horizons? Are there readily-modifiable parameters (spacecraft mass, CoG, orbit, planetary gravity, etc) that can be changed to make this a relatively easy transtion to another spacecraft? Seems a waste to develop these tools from scratch for each mission! - submitted by Ken Reed, Interested public, 02-06-2012

Every NASA mission is unique, and it is not possible to build a single tool for all missions. However, SciBox is built to permit some level of system reuse. We have systematically separated software components that are specific to MESSENGER from the generic SciBox software library. The idea is that we can use the library to rapidly customize another MESSENGER-like planning system for other missions. Prior to MESSENGER, SciBox was demonstrated on other space missions, but only for a single instrument. MESSENGER is the first mission to fully utilize SciBox for the entire science operation.

--Teck Choo, Johns Hopkins University Applied Physics Laboratory
MESSENGER Science Operations Center

At what frequency does the data dump link from MESSENGER to the ground station of the Deep Space Network operates? Is it S-Band or Ku-Band? What is the exact frequencies of transmission both for forward link and return link? Thanks for your response, and have a good day. 

- submitted by George W. Raffoul, 01-18-2012

MESSENGER has X-band (8.4 Ghz) phased-array antennas. You can read more about the communications system in papers by Dipak K. Srinivasan and colleagues published in
2005. These papers are available on the publications portion of the MESSENGER website.

-Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Was the MESSENGER spacecraft damaged by the recent intense CME toward Mercury? - submitted by Richard Harris, 12-13-2011

Coronal mass ejections (CMEs) are generally not harmful to the spacecraft. See two previous questions on the topic here and here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What is the maximum mass of MESSENGER? How much energy (thrust) was required to move MESSENGER into space? How will MESSENGER land safely on Mercury? Or can it land on Mercury? - submitted by James, High school student, 11-18-2011

MESSENGER is an orbiter, not a lander. Information on the mission design and propulsive maneuvers can be found here. You can read more about the spacecraft's propulsion system and fuel load. You may also wish to read this publication that gives more information on the spacecraft (scroll down to "Saranto, A.G.).

David Blewett, Johns Hopkins Applied Physics Laboratory
MESSENGER Participating Scientist

Dear Sir, I am an Aeronautical Eng. I am very much interested in Messenger Spacecraft. Actually i would like to model (macro-model) this spacecraft ( Soft model). I will be very thankful to you, if you can provide me such related answers, such as 1) The surface area of the plate (for example, the area of the solar panel). 2) The optical properties of each plate: the reflectivity and absorptivity coefficients of each plate. And also need the coordinates of the center-of-mass and of the center-of-phase of the high gain antenna and the mass of the spacecraft. Thanks

- submitted by Ashok Verma, Interested public, 10-05-2011

Public release of certain spacecraft data is prohibited by law; see this previous question. Refer to this question for links to the many websites and publications that do give information
about the spacecraft.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

A) Can you please tell me about how an orbital course is decided and justified. What are the factors to be taken under consideration for tracing an orbit around Mercury. Can you also provide an example in order to explain this question.  B) Please explain how electronics were protected from geomagnetic storms. Will Faraday cages work?  C) How is MESSENGER insulated to protect it from heat and radiation. D) Will the Mercury's magntic field affect any device on MESSENGER? E) How do propulsion systems work when there is nothing to provide a reaction force in space and propel it forward during orbit insertion. - submitted by TJ, High school student, 09-01-2011

A) A previous question covered this topic.

B) See this and this in the Q&A archive.

C) Read about MESSENGER's sunshade.

D) Mercury's magnetic field is about 100 times weaker than that of the Earth. The only thing on the spacecraft affected by the magnetic field is the magnetometer, designed
to measure the field!

E) Rocket propulsion operates according to Newton's laws of motion.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

For engineering: Do the charged particles in the solar wind create differential charging on different parts of the spacecraft? 

- submitted by Henry Barru, Interested public, 08-26-2011

Charged particles in the solar wind do impart a charge to the spacecraft. This leads to a bulk steady-state charge bias on the surface of the spacecraft. However due to both the selection of slightly conductive materials for the outer surface of the spacecraft combined with a very hot operating environment, there is sufficient surface conductivity to limit the accumulation of differential charging across the spacecraft.
--Eric Finnegan, Johns Hopkins University Applied Physics Laboratory
MESSENGER Mission and Spacecraft Systems Engineer

From: william plowden
Thank you for responding! Yet the answers are a bit vague, and understandably so. By "radiation hardened", I think you mean the developed equivalent of "nuclear hardened" and can grasp a Faraday cage kind of thing. It's the phrase "space qualified" that gets me.

Of course MESSENGER is bombarded by all kinds of stuff that generate eddy currents and breaks or changes chemical bonds and rattle it severely. It's really close to a colossal fusion reactor belching out EM bursts and ion jets. With something to somewhat bounce off of and generate stimulated emissions, coming back from another angle. Define "umbrella". How does the umbrella take the abuse and still function thermally and chemically? How does it vent what it gets? How does the stuff the umbrella can't protect against deal with the residual EM radiation and ion influx? I guess what I'm asking isn't allowed to be answered, or hasn't been condensed and simplified to the point that it's relevant to my limits.

Over all, my curiosity is led by the way in which something can function in a nuclear reactor, saturated across the spectrum, bombarded by plasma cutters of diverse energies from various possible directions; going from near zero K to titanium ionizing temps and still last and transmit good info. How do you do it? - entered by Q&A admin, 08-16-2011

Let me start with Space Qualification. It refers to a wide range of tests and analyses to prove that individual components and built-up assemblies are reliable and able to withstand the rigors of a space mission. Qualification tests includes such things as vibration to high levels, temperature cycling, which for individual components is usually between -55C to +125C, hermeticity tests, voltage range tests, radiation hardness, etc. 100% of all components must pass these tests to be used on the mission.

Radiation hardness is divided into two areas: total dose, and single event effects. Total dose measures the amount of radiation energy that can be deposited into the component before it fails to operate as intended. It is measured in Rads. The level of total dose hardness required depends on where the mission will operate. A mission to the magnetos[here of Jupiter will need a hardness of several hundred thousand or a million Rads, while a mission to low Earth orbit may only require several thousand Rads. For MESSENGER, the combination of cosmic rays, energetic solar particle events, and energetic particles in the Mercury magnetosphere, mean that a radiation hardness of several tens of thousands of Rads is required.

Single event effects refers to a range of effects such as "bit-flips", where an individual high energy atomic nucleus may hit a single transistor in an integrated circuit and change its state to the opposite one (from "on" to "off" or the reverse. There are a range of other single event effects that can destroy components or produce incorrect operation.

Radiation resistance in components is something that is designed into the parts through careful attention to the geometry and chemical make up of the individual transistors in the circuit. Even then, one is never sure of its actual radiation hardness without giving it the full range of tests. As integrated circuits get more complex and the individual transistors have become much smaller, it has becomes much more difficult to build in radiation hardness. So, the choice of components has become more restrictive.

Some weakness in radiation hardness can be compensated by adding shielding to lower the exposure of the components to the radiation environment. However, on missions like MESSENGER, where every extra gram threatens to make it impossible to reach Mercury orbit, the individual parts must be inherently radiation hard.

Rob Gold, Johns Hopkins University Applied Physics Laboratory
MESSENGER Science Payload Manager

What is the equivalent conic accuracy of each of the sensors alone, and what is there final accuracy after interpolation and HDR processing among the sensors? In particular, the spectroscopy and neutron detectors combined with the surface radar and other cameras. - submitted by william plowden, Interested public, 07-14-2011

With the exception of MDIS, all of the instruments are directly mounted (fixed) to
the spacecraft body. The MDIS wide and narrow angle cameras are attached
to opposite sides of an articulating platform which affords greater
freedom to image the surface while keeping the spacecraft safe. For those
instruments directly attached to the body, the accuracy of pointing
reconstructions are impacted primarily by our knowledge of two factors:
the error in the spacecraft orientation estimate and the alignment of the
instrument's mount. MDIS adds the additional complication of modeling the
motion of the articulating platform which introduces another error source.

Detailed measurements of the mounting alignments were made prior to launch
as the instruments were attached to the spacecraft. For several sensors
these errors are substantially less than their angular sensitivity. Each
of the remaining instruments have them or their in-flight calibration
updates folded into the pointing reconstruction process to account for the
misalignment. While these errors vary from instrument to instrument,
generally they are measurably smaller than the uncertainty in the
knowledge of the spacecraft's orientation. This source of error is
roughly 300 microradians (0.017 degrees) though it is often less than
this. With the MDIS cameras the total pointing reconstruction error is
increased by another 50-75 microradians due to uncertainties in our model
of the articulating platform's motion. These sources are not usually
additive due to the nature of rotations, but combining them in this way
provides an upper limit on the total error.

--Scott Turner, Johns Hopkins University Applied Physics Laboratory
MESSENGER Science Operations Center

What effects does the radiation have on the systems? What wavelength EM spread does the main shield protect against? How does MESSENGER protect itself from solar flares and EM bursts outside the shielding's limits? How long can the electronics and materials take this abusive environment before failure? - submitted by william plowden, Interested public, 07-14-2011

MESSENGER's Sun shade is for thermal shielding (to protect the spacecraft from the light and heat of the Sun, just like using an umbrella on a sunny day). The spacecraft is also bombarded by charged particles from the Sun (e.g., coronal mass ejections) as well as solar and galactic cosmic rays. Spacecraft use "space-qualified" components and "radiation-hardened" electronics to avoid the effects of this bombardment.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Are there scale, preferably dimensioned, external drawings of the MESSENGER spacecraft available from which a small model could be constructed? - submitted by arthur krull, Interested public, 05-05-2011

Because the US government has classified spacecraft as controlled items under the Export Administration Regulations, we have not released dimensioned drawings of the MESSENGER spacecraft. The best available images approved for public release are in the MESSENGER book and various scientific presentations. However, they do not show actual dimensions.

You can find a MESSENGER paper model here.

--Rob Gold, Johns Hopkins University Applied Physics Laboratory
MESSENGER Science Payload Manager

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Is MESSENGER equipped to track objects from space that are going to collide with Mercury? and can real time pictures be taken if such an event were to happen while MESSENGER is in orbit? - submitted by John Stewart, 04-26-2011

MESSENGER's cameras, spectrometers, magnetometer and altimeter are full scheduled through a complicated optimization process to maximize the observations of the planet during the one Earth-year primary mission. The cameras are working to obtain a high-resolution global morphology basemap (~250 meters/pixel) and a stereo complement, global 8-color mapping at about 1 km/pixel, very high resolution imaging of hundreds of special targets, campaigns to map the polar regions and monitor illumination changes as Mercury rotates, and observations of the limb to help define topography. Discovery and monitoring of meteoroids that could collide with the planet were not part of the baseline science plan for the mission. There is no on-board capability to perform real-time tracking of moving objects.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

At some point during the mission I assume the the Sun will come between Mercury and Earth? If this is happens, how does information from MESSENGER reach Earth? - submitted by Aaron, College student, 04-05-2011

We refer to such an arrangement of Mercury and Earth with respect to the Sun as a Superior Solar Conjunction (as opposed to Inferior Solar Conjunctions, in which Mercury is between the Earth and the
Sun). These are generally of very short duration now since Mercury goes around the Sun quickly relative to the Earth's view. Early in the mission (during cruise) we had some that were over 30 days long, in which we could not communicate with the
spacecraft for several weeks right in the middle of those periods (usually within about 1.5 degrees on either side of the Sun). Now they are only a couple of days long, and typically the peak periods occur outside of our planned contacts
with the Deep Space Network anyway. As a result, there is little impact to operations now, with perhaps just a day or two where we have to curtail our activities due to the risk of degradation to our communications due to interference
from the Sun. The next one will occur in early June .

--Andy Calloway, Johns Hopkins University Applied Physics Laboratory

MESSENGER Operations Team Manager

What was the instrument on MESSENGER that guided and controlled the spacecraft in the place where the MOI was possible and eventually successful? Did APL make this instrument? - submitted by Ken Aiello, Interested public, 03-31-2011

Navigation is chiefly through tracking of the spacecraft's radio signal. More about the communications system is given at this page.
The guidance and control section of the webpage describes how the spacecraft senses it's orientation, crucial for properly pointing the cameras and other instruments, and for keeping the sunshade in the right orientation.
Check the Team page to see which organizations in which U.S. States or foreign countries contributed to MESSENGER in various ways.

A. Is there any live telemetry available on the web?   B. Are there any readings from the temperature on the heatshielding? If it conformed to the expected value etc.    Impressive work! // Regards - submitted by David Lundberg, Interested public, 03-30-2011

There is no spacecraft telemetry available on the web. We do not have any direct readings from the sunshade. However, the temperature performance of the spacecraft indicates that the sunshade is working as intended to keep all the instruments and systems at their expected temperatures.

--Jack Ercol, Johns Hopkins University Applied Physics Laboratory

MESSENGER thermal engineer

What can you tell us about the imaging instruments used by MESSENGER? Why for example are the images released so far grayscale? What other types of images might we expect to see during it's mission? - submitted by JP, Interested public, 03-30-2011

Information on all of MESSENGER's instruments can be found here.

A scientific multispectral imager like MDIS's Wide Angle Camera operates by snapping images through different filters that each pass a relatively narrow range of wavelengths. The result is a set of images for a particular area on the surface - one in violet light, one in blue, one in green, and so forth. Each of these is a grey-scale image. When the images are co-aligned, they form a data product called an "image cube" (because it has two dimensions of spatial information, and one of spectral (color) information). We can process the image cube in various ways, for example to emulate "true color" seen by the human eye, or to emphasize various color characteristics that are related to the composition of the surface. To the human eye, Mercury would appear to be greyish-brown in color (not much different than greyscale).

The MDIS Narrow Angle Camera is a monochrome imager - it has no filter wheel. But the NAC optics produce higher spatial resolution than the WAC so that the morphology of the surface can be examined in more detail.

You may be interested in a technical paper by Ed Hawkins and colleagues, published in 2007, that gives all the details for MDIS.

Browse our Image Gallery to get a taste of the kind of image products that will be produced during the primary mission.

--Dave Blewett, Johns Hopkins University Applied Physics Lab

MESSENGER Participating Scientist

Q1..How are you able to send and receive picture data from 5 billion miles away?Q2..What type of signal and equipment is being used to send that data? Q3..How long does it take to receive data from the moment of capture ? - submitted by Talan M, 03-30-2011

Radio waves (X-band) work just fine, as long as there is a strong enough signal transmitted and a capable antenna to receive it. More on the communications system can be found here.

Radio signals travel at the speed of light. At the time of orbit insertion on May 18 (UT), 2011, the one-way light time between Earth and Mercury was about 9 minutes. However, data is not transmitted immediately after it is collected by one of the instruments. It is stored in the spacecraft's solid state memory recorder, and is downlinked when a track with NASA's Deep Space Network is scheduled. Generally there will be one DSN contact per day.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

I have 3 questions about comms:

a) How is communication between MESSENGER and earth handled? in terms of getting hi-res photos back, that should be quite slow? b) Are the different means of comms like data and control / primary or secondary. c) Finally, what is the daily power consumption of the craft and what is the output power of the (various?) transmitters for comms.   Many thanks. - submitted by Crispin Proctor, 03-30-2011

A) MESSENGER has a fully redundant on-board communications system that handles all of the communications between the Earth and the Spacecraft. On the Earth, we use the large 34-meter and 70-meter antennas operated by the NASA Deep Space Network (DSN). On board the spacecraft, we have two radios, two power amplifiers, and a suite of eight antennas to send and receive signals. In terms of speed of the communications link, that varies over to course of the mission. When Mercury (and MESSENGER) are on the far side of the Sun, the distance is quite a bit larger and our data rates are lower. When Mercury is closer to Earth (on the near-side of the Sun), we have a shorter distance and can therefore support a higher data rate. MESSENGER's maximum data rate is 104 kbps.

B) We have many different operating modes for the communications subsystem. When everything is going normally, we communicate with a phased-array high-gain antenna. That allows us maximize our data rate. In an anomalous situation, the spacecraft might not know where the Earth is, and is incapable of pointing the high-gain antenna back at Earth. In that case, we use a fanbeam, or medium-gain, antenna. The data rate becomes very slow -- 10 bps. But, it allows us to establish a communications link to the spacecraft and start our troubleshooting efforts to get the spacecraft back up and running. Lastly, when we have a major maneuver (such as Mercury Orbit Insertion), the propulsion system dictates the pointing, and we end up using low-gain antennas. Low-gain antennas are very useful because the spacecraft can be in nearly any orientation, and the broad-beam nature of these antennas will still enable a low-power link.

C) For our transmitters, each consumes roughly 45 W of power, and provides almost 12 W of radio frequency (RF) energy to be transmitted back to Earth.

--Dipak Srinivasan, Johns Hopkins University Applied Physics Laboratory

MESSENGER Communications/RF Lead Engineer

How long does it take for electronic signals and commands from Earth to get to MESSENGER? Similarly, how long does it take for a scientist here on Earth to receive something like an image from MESSENGER? Considering the distance, I would imagine there there is a time lag between sending and receiving signals or images, and I'm curious how that is taken into account. If you need to fire off an engine to change trajectory at a certain time, do you have to send out that signal a few earth hours or days in advance? - submitted by MESSENGER_fan, Interested public, 03-30-2011

Communication with MESSENGER is by radio waves, which travel at the speed of light. At the time that MESSENGER entered orbit around Mercury, the one-way light time between Earth and Mercury was about 9 minutes. The mission operations team does not "drive" the spacecraft in real time. Instead, sets of commands are uploaded to the spacecraft's computer days or weeks ahead of time for execution later. Learn more about communications with the spacecraft here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Where can we learn about the specifics of the hardware in the MESSENGER craft? CPUs, Camera resolutions, Power management and Software/system architectures? - submitted by John R, 03-29-2011

Hello - A wealth of information on the spacecraft and instruments can be found on the MESSENGER website. Also, team members have described the hardware in a variety of conference presentations and publications.

WHAT WAS AVERAGE SPEED OF MESSENGER ON ITS TRIP TO MERCURY? - submitted by steve wiggins, Interested public, 03-21-2011

what is the fuel for the main rocket engine - submitted by Xavier, High school student, 03-20-2011

Read about the propulsion system here.

I think of space as being very cold (< -300 degrees) yet it is constantly mentioned about the difficult thermal environment around Mercury. What is the ambient temperature around the spacecraft while in orbit and how much does it vary between apogee and perigee?

Are there any graphics out there showing the temperature decline as you move farther from the Sun? The temperature obviously declines rapidly to go from the millions of degrees of the corona to the temperature of space outside the ISS but how fast does it decline?  Thanks - submitted by Terry Gordon, Interested public, 03-20-2011

Space, being a vacuum, has no temperature. What matters is the distance between a source of radiant heat and the surface of interest. For example, the distance from the Sun to a spacecraft (or planet), or the distance between a stove burner and your hand. The amount of energy hitting a surface decreases as the inverse of the distance squared (this is the "1 over R-squared" law). The temperature that a surface will reach is determined by the balance between the amount of energy that the surface absorbs and the amount that it radiates away. If a dark surface and a highly reflective surface are at the same distance from the Sun, the dark surface will absorb more light and hence will have a higher temperature.

The Sun gives off light and other forms of electromagnetic radiation as if it was an "ideal radiator" with a temperature of about 5800 K. MESSENGER has a sunshade to protect itself from the Sun's intense radiant heat at Mercury's distance. But the spacecraft must also deal with the sunlight reflected up from Mercury, and infrared heat emanating from the planet's scorching day-side surface. Managing this thermal load is one reason that MESSENGER is in a highly elliptical orbit, dipping briefly to as close as 200 km above the surface but then moving out to as much as 15,000 km away from the hot planet.

With respect to the kinetic gas temperature of the Sun's extremely thin outer atmosphere (corona) and the decrease in temperature of the tenuous solar wind with distance: There has been theoretical work trying to model the radial dependence of the solar wind temperature from the corona all the way to interplanetary space. From these models, the predicted solar wind temperature has a maximum at around 3 solar radii and decreases as distance to the minus 0.4 to 0.8 power, depending on the particular solar wind conditions (further, temperatures differ for solar wind electrons vs. protons). When extrapolated to the distance of Earth, the predictions agree well with local measurements of the solar wind temperature (~100,000 K).

--David Blewett, MESSENGER Participating Scientist

and George Ho, Instrument Scientist for the MESSENGER Energetic Particle and Plasma Spectrometer

Johns Hopkins University Applied Physics Laboaratory

Where will MESSENGER go after its year long mission around Mercury? - submitted by Gerald Schuler, Interested public, 03-19-2011

The entire team is looking forward to a successful primary mission (one Earth year in length), and is hoping that
NASA will approve an extended mission for another Earth year. There should be enough fuel remaining at the end of the primary mission to maintain the orbit against perturbations from the Sun's gravity for another year of operations. However, at some point MESSENGER will run out of propellant and will be unable to maintain its orbit; it will eventually crash into the surface of Mercury. Perhaps the European Space Agency's BepiColombo orbiter, scheduled to arrive at Mercury a few years after MESSENGER's mission is complete, will be able to find a tiny new crater - formed from MESSENGER's impact.

--David Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

What material(s) are being used to shield the craft and its electronic payload from the intense heat and radiation? - submitted by Anton, Other educator, 03-19-2011

Thermal control was a major consideration in designing the spacecraft. The sunshade, made of woven ceramic cloth, is a key component for maintaining the spacecraft at the proper temperature.

Because Mercury is so close to the Sun, I'm surprised the MESSENGER spacecraft is able to orbit around Mercury without burning up. How do you protect the spacecraft from the heat? - submitted by S. L. Weakley, Other educator, 03-18-2011

Thermal control was a major consideration in designing the spacecraft. The sunshade, made of woven ceramic cloth, is a key component for maintaining the spacecraft at the proper temperature.

What special meaures were needed to protect MESSENGER from the Sun? Even around Earth we can see damage to satellites from CME (coronal mass ejections). MESSENGER is MUCH closer and perhaps there is no magnetic field to deflect the CME.

Dave Wagner, Lake County Astronomical Society - submitted by David Wagner (Lake County Astronomical Society), Other educator, 03-18-2011

You can read about the spacecraft's thermal design here.

With respect to radiation tolerance, most of the effects of CMEs (coronal mass ejections) result in the emission
of low-energy plasmas, which can not penetrate into the spacecraft. However,
solar flares and the interplanetary shock waves that are generated by some
CMEs can accelerate protons and heavier atomic nuclei to much higher
energies. Since the electronics are inside the spacecraft and in their own
metal boxes, it takes particle with energies of greater than about 10
million electron volts to even reach the sensitive electronics.

Specially designed transistors and integrated circuits can withstand
relatively high doses of these particles. On a mission like MESSENGER, every
component (transistor, resistor, capacitor, inductor, etc.) is tested to
ensure that it can withstand the expected radiation dose from solar
particles and cosmic rays with sufficient margin to ensure a successful
mission. Since MESSENGER has gone close to the Sun, where there is limited
experience of the actual radiation dose, we had to use theoretical models to
predict the expected dose and test the components to the levels predicted by
those models.

--Rob Gold, Johns Hopkins University Applied Physics Laboratory

MESSENGER Science Payload Manager


How is it possible for the MESSENGER to almost fly 5 billion miles without refueling?

My other question is what will happen to the MESSENGER spacecraft after its year long mission? Thanks!! "Skippii"

- submitted by Ryan McLaurin, High school student, 03-18-2011

A spacecraft that uses a chemical rocket for propulsion is not firing that rocket the entire time that the voyage is underway. MESSENGER spent most of the time on the way from Earth to Mercury coasting, subject only to the gravitational pull of the planets and Sun, and the forces of solar radiation pressure. During MESSENGER's cruise, the main engine was used for only five major "deep space maneuvers" to make changes to the spacecraft's trajectory, and of course it was fired again for about 15 minutes to slow MESSENGER for capture into Mercury orbit in March 2011. Lots of detail on this topic is available on the Mission Design webpage.

Following its Primary Mission, the team hopes that NASA will approve funding for an Extended Mission of one additional Earth year. Not long after an Extended Mission ends, MESSENGER will no longer have enough fuel to be able to maintain its orbit. It will impact the surface of Mercury a few years later.

--David Blewett, Johns Hopkins University Applied Physics Laboratory,

MESSENGER Participating Scientist

When was the spacecraft first designed? When and where did construction begin? How long did construction take? - submitted by Steven Van Loon, 03-18-2011

The MESSENGER concept for a Mercury orbiter was first designed in the spring
of 1996 and proposed to NASA as a Discovery mission. It made it through the
first level of selection, but was not chosen for development because NASA
was not convinced that we thoroughly understood the thermal problems of a
Mercury mission. We continued to develop the concept and re-proposed it to
NASA in 1998. NASA was finally convinced that MESSENGER would work, and real
detailed design began in January of 2000. The spacecraft was designed,
built and hardware qualified by early 2004. The rest of 2004, through July, was
spent in testing. MESSENGER was launched August 4, 2004.

The spacecraft was built at APL. However, many of the components and
instruments were built by other organizations across the U.S. and some from

--Rob Gold, Johns Hopkins University Applied Physics Laboratory

MESSENGER Science Payload Manager

What is the current velocity of the spacecraft, prior to the orbital capture burn? I understand that the burn will slow the spacecraft down by over 1900 mph. - submitted by Roamin Gnome, Interested public, 03-17-2011

Just prior to the burn on 2011 March 18 00:45:15 UTC the magnitude of the spacecraft's velocity relative to Mercury was 4.459 km/s or 9974.163 mph.


--Dawn Moessner, Johns Hopkins Applied Physics Lab

MESSENGER Mission Design Team

Hi: Do you guys configure spacecraft fault protection in such a way as to minimize a safe mode engine shut down at the time of orbit insertion?   Thank You. - submitted by Chuck Hunt, Interested public, 03-16-2011

Although it seems counterintuitive we do disable most of our Fault Protection during orbit insertion to maximize the likelihood of completing the insertion and minimize the chance of a false trip or unrelated fault from prematurely aborting the insertion maneuver. However, the spacecraft does not completely ignore faults. Rather, it still monitors for faults during Mercury orbit insertion, but it defers taking any potentially interfering or corrective action until the maneuver has completed.

--Adrian Hill, Johns Hopkins University Applied Physics Lab

MESSENGER Fault Protection/Autonomy Team

How much fuel did fire sailing save? How will that savings affect the mission? Will you fire sailing in orbit?

Question from mrwmurphr. - entered by Q&A admin, 03-04-2011

1) How much fuel did fire sailing save?
2) How will that savings affect the mission?

I was able to find a headline in the news stating that MESSENGER was 'Sailing on the Fire of the Sun,' so I can understand the reference to "fire sailing." However, we use the term "solar sailing" which refers to our use of radiation (light) pressure from the Sun to control the momentum accumulation on the spacecraft, as well as to adjust the spacecraft's trajectory. The benefit of solar sailing is in the ability to place the spacecraft at almost the optimum point for each of the planetary flybys, ensuring that MESSENGER received the best gravity assist to slow down on approach for the March 18th orbital insertion. When the mission was planed, the mission had ~15% additional maneuver capability than it needed to complete the mission. Approximately 2/3 of this was expected to be used to adjust the trajectory of the spacecraft over the 6.5 years in cruise and the 1 year in orbit. When we instituted solar sailing (just prior to the first Mercury Flyby in December 2007) we had consumed ~1/3 of this expectation (or ~5% of the reserve maneuver capability). Therefore from the initial design, solar sailing has saved ~5% of the reserve maneuver capability. Further, since launch the spacecraft has performed all main engine burns flawlessly and our trajectory design teams have refined the spacecraft's trajectory such that the 15% additional maneuver capability has been restored, providing the potential to operate in orbit around Mercury for much longer after the end of the initial year of study.

3) Will you be fire sailing in orbit?
Although we will use solar radiation pressure to assist in the management of the spacecraft momentum and control of the orbit around the planet, the effectiveness will be greatly reduced compared to cruise. Solar sailing is effective during the inner cruise portion of the trajectory, since the orientation of the spacecraft relative to the Sun can be controlled by our guidance navigation and control engineers almost exclusively to optimize momentum and trajectory adjustments. When in orbit around Mercury, the primary mission objective is to collect information about the planet, so the attitude of the spacecraft is dedicated to the needs of the science instruments. Hence the various instrument teams place the boresights of their instruments on or around the planet, limiting the effectiveness of solar sailing.

-Eric Finnegan, MESSENGER Mission and Spacecraft Systems Engineer.

Questions about Mercury's orbit, rotation, and place in space

Who discovered Mercury? - submitted by Opoka john modi silvio, High school student, 04-21-2016

The planet Mercury is visible to the unaided eye, and thus has been known by humans since ancient times. It is one of the five planets known to ancient people: Mercury, Venus, Mars, Jupiter and Saturn. Mercury was the last of these planets to be studied by an orbiting spacecraft.

- - Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

hi em sintle from pakistan i wan to complete my asignment here my question is what time mercury take to circle the sun - submitted by sintle rose, College student, 03-15-2016

It takes Mercury 88 Earth days to go around the Sun. The length of the day on Mercury is 58 days with respect to the fixed stars, but it is 176 days from noon to noon. To read more about these topics, see the links in this Q&A. See also this animation that illustrates Mercury's motion around the Sun.

--David Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist


Why are Mercury and Earth different sizes? - submitted by Caroline C, Middle school student, 12-05-2015

A range of evidence indicates that our Solar System formed about 4.6 billion years ago from a cloud of gas and dust that contracted under gravity, with the central concentration of matter forming the Sun. Clumping of solid material within the rotating disc that surrounded the proto-Sun led to growth of planetesimals, rocky pre-cursors that underwent mutual collision, break-up, and re-accretion events. Higher temperatures closer to the Sun led to formation of the rocky inner planets (Mercury, Venus, Earth, and Mars), whereas the outer Solar System came to be dominated by volatile compounds - in the gas giant planets (Jupiter, Saturn), the ice giants (Uranus and Neptune), and the multitude of icy comet-like bodies in the Kuiper Belt (Pluto is the most well-known example) and the Oort Cloud.

Thus, the size of each of the planets, their locations, and compositions are the result of physical processes and random variations that took place as the Solar System formed and continued to evolve.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Have any 'Peaks of Eternal Sunlight' been discovered at either of Mercury's poles? - submitted by Bryce Johnson, Journalist, 09-01-2015

Both the Moon and Mercury have a low obliquity (obliquity is the tilt of the rotation axis relative to the orbital plane). Therefore, the seasonal differences in solar insolation are small. The solar incidence angle in their polar regions only varies sightly, which allows deep crater floors to be in permanent shadow and high peaks to potentially be constantly sunlit. While large areas have been unequivocally identified on both bodies to be in permanent shadow, we know with certainty that no peak of eternal light exists at the Moon (although a very few locales can be illuminated for >250 continuous days). The case is not closed on Mercury, because we have limited temporal and spatial coverage from the MESSENGER camera (MDIS), and only reliable topographic data in the northern polar region from the altimeter (MLA). Furthermore, the northernmost latitudes, most likely to host 'peaks of eternal light', could not be extensively covered by the altimeter because of the 84-degree inclination of MESSENGER's orbit. Special spacecraft operations were required to sample them, and the data coverage is not as uniform as below 84 degrees North. Nevertheless, numerical modeling of the illumination with the current topographic maps does indicate that the rim of Tryggvadottir, the crater closest to the north pole, could host some peaks of eternal light. It is an intriguing possibility, which will need to be ascertained with future studies.

--Erwan Mazarico, NASA Goddard Space Flight Center
MESSENGER Geophysics Discipline Group

Describe the path of the sun over the course of one day in mercury - submitted by william, High school student, 08-06-2015

Sounds like a question on a homework assignment or take-home test. The MESSENGER website Q&A page contains answers to previous similar questions. Browse the "Mercury In The Solar System" category, and especially answers to these two questions. Be sure to click on the links in those answers to be taken to the MESSENGER Education pages where there are cool animations that illustrate the motion of the Sun in Mercury's sky.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How and who, or what, created the planet we all now know as Mercury.Is it an escaped moon from Venus?Thank You. - submitted by No Name, Elementary school student, 05-18-2015

All the planets in our Solar System, including Mercury, were formed about 4.5 billion years ago from a cloud of gas and dust (called the solar nebula) that surrounded the early Sun. The processes in the nebula that led to planet formation are not completely understood, but new information on the composition of the planets (like that obtained by MESSENGER for Mercury) help to constrain mathematical models for planet formation. Astronomical observations of extra-solar planets and of planet-forming regions around young stars elsewhere in our galaxy also lend key information on how planets form. One of the main questions about Mercury prior to MESSENGER is why the planet is so dense - that is, why is Mercury's iron core so large in comparison to its rocky outer layers relative to the other inner planetary bodies (Venus, Earth, Moon, Mars). MESSENGER's measurement of the high abundance of volatile elements like sulfur and potassium demonstrates that certain formation mechanisms for Mercury that involve high-temperature events are not plausible. This is bringing about reconsideration of the hypotheses for Mercury's formation. The finding that Mercury is volatile-rich is considered to be the #1 top science discovery of the mission: see this link and scroll down to "Number 1. Volatile-Rich Planet".

It is extremely unlikely that Mercury is an escaped satellite of Venus. See this previous Q&A for a discussion.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How do I get to the ability to point my finger to where Mercury is at this moment. Cheers. - submitted by Trevor Nalliah, 05-15-2015

There are a variety of planetarium programs for personal computers, and also smart-phone apps, that can help you to locate objects in the night (or daytime) sky. Magazines like Astronomy and Sky and Telescope have monthly columns on the deep-sky and Solar System objects that are favorably located for observing. You might also check the websites of those publications.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

what has been the hottest and the coldest temperatures ever recorded on mercury Thanks - submitted by Felipe, Middle school student, 01-30-2015

MESSENGER does not carry any instrument (such as a thermal infrared radiometer) that can directly measure surface temperature. However, physical modeling indicates that temperatures within permanently shadowed craters near the poles can drop as low as 50 K (-370° F). See this set of presentation materials for information on MESSENGER's study of Mercury's polar regions, and a map of model surface temperatures.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I'm a high school student and have done my senior project on how observing Venus and can tell us about global warming on Earth. On researching Venus's slow rotation I came across an interesting article on how Mercury may have been a lost natural satellite of Venus, Venus an ultra-slow rotation period and Mercury it's highly eccentric orbit. Is this theory at all possible, and if so when did these two bodies separate and why? - submitted by Suzuki, High school student, 11-10-2014

A few comments on the hypothesis that Mercury could be an escaped satellite of Venus. The idea was first suggested (and rejected) by Harold Jeffreys in 1918 (On the early history of the solar system. Monthly Notices Royal Astron. Soc. 78, 424).

While Venus could have lost its initial rotation by the tidal evolution and escape of a satellite, solar gravitational and thermal tides alone are sufficient to account for its present slow rotation.

With its eccentric orbit, Mercury at aphelion is still a long way (0.25 AU) from Venus (with a nearly circular orbital radius of 0.72 AU). This makes it unlikely that the orbit of Mercury ever intersected that of Venus, although it can't be ruled out. Chaotic resonances due to interactions with the giant planets allow orbital changes of this magnitude over long enough times. Detailed calculations suggest that the probability is only about 1% (J Laskar & M Gastineau. 2009. Existence of collisional trajectories of Mercury, Mars and Venus with the Earth. Nature 459, 817 and references therein).
--Steven Soter, American Museum of Natural History

Is it at all possible that Mercury has a yet-undiscovered moon orbiting it? I'd assume it would be small, like a captured vulcanoid, and probably the size of Deimos if not smaller. I've heard about the Mariner 10 incident where a Mercurian moon was briefly believed to have existed, but has there been any similar incidents with MESSENGER, such as unexplained "tides" on the surface or axial wobble associated with a natural satellite? If Mercury does have a moon what's the biggest it could possibly be in order to avoid detection so far, and if found what would we name it (Vulcan would be a good common name but scientifically would it be called S/2015 M1 or S/2015 H1)? - submitted by Suzuki, High school student, 11-10-2014

We often get questions about searching for moons of Mercury or vulcanoids. See this previous question in the MESSENGER Q&A website.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I have difficulty visualizing this sort of thing, even though I know Mercury's rotation rate. Maybe you can help: Suppose someone was out on Mercury's surface at 'high noon' The Sun would be directly overhead (at zenith?) How long would it take for the Sun to move from the noon position to the 'one o'clock' position? - submitted by Bryce Johnson, Journalist, 04-10-2014

The motion of the Sun in Mercury's sky results from a combination of the planet's rotation on its axis and the travel of the planet around the Sun in its elliptical orbit. Near noon, the motion of the Sun will pause and briefly reverse before proceeding again towards setting. Additional explanation is given here. This animation may also help. You can start the motion of the Sun across the sky, and hit Stop (on the right middle) at any point. The counter shows the elapsed number of Mercury rotations and Earth rotations. So you can see approximately how long it takes for the Sun to move a given angle in the sky.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

what is the temprature on Mercurys terminator? - submitted by Robert, Elementary school student, 04-06-2014

Airless planetary bodies in the inner Solar System (like Mercury, the Moon, asteroids) are subject to wide temperature swings as they rotate. The surface begins to be warmed by sunlight once the Sun rises, heating continues throughout the day, temperatures begin to decrease in the late afternoon, and plunge quickly once the Sun sets. Without the effects of an atmospheric "blanket" to help moderate temperatures between the day side and the night side, un-illuminated surfaces cool by emitting infrared radiation (heat) to the darkness of space, and the surface can become very cold. As you can imagine, the exact high and low temperatures and the rate at which temperature changes will vary with factors such as the body's distance from the Sun, how fast it rotates, and the location on the body (chiefly the latitude). For Mercury, the combination of being a slow rotator (the length of Mercury's solar day is 176 Earth days) and orbiting so close to the Sun means that Mercury has an extreme range of temperatures: a high of roughly 700 K (800 deg. F) on the daytime equator to a low of about 90 K (-300 deg. F) on the night side. (Note that in permanently shadowed portions of polar craters, temperatures are even lower, and have probably remained so for a billion years or more.)

The terminator is the line between day and night, that is, the instantaneous line of longitude where on one side the Sun is above the horizon and on the other the Sun is below the horizon. Of course, because the Sun is not a point of light but has a finite diameter (the Sun in Mercury's sky appears about 2.5 times larger than it does in the sky viewed from Earth), there is a period of time when the disc of the Sun is partly below the horizon and partly above. When the Sun is so low in the sky, objects like scarps or crater rims cast very long shadows. So the temperature of a particular spot on the ground has a complicated dependence on the local topography. But generally, a place on the terminator moving from night into day will be warming up from near the maximum low temperature. A place moving from day into night will have already cooled from its maximum temperature, with the temperature decreasing quickly once it is in a shadow cast by topography or it has moved entirely into the night side.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Is it true that Mercury's unique spin-orbit 'coupling' would allow an astronomer to observe the entire universe over the course of a single night? Also, for observing specific objects, is it true that Mercury's rotation would allow up to 44 days observing time? Thank you. - submitted by Bryce Johnson, Journalist, 01-28-2014

Mercury's 3:2 spin-orbit resonance causes some interesting effects, and the length of daytime or nighttime is not as straightforward as one might think from our experience on Earth. While Mercury rotates on its axis every 58.6 Earth days, it takes Mercury 87.9 Earth days to do one complete revolution about the Sun. As a result, a "solar day" on Mercury, i.e., the period of time from which the position of the Sun in the sky at a given, fixed Mercury longitude returns to that same position is 176 Earth days. Therefore, the length of darkness ("night time") would be half of that, or about 88 Earth days. This can be demonstrated by going to this link and playing the animation. Notice the Stats numbers in the lower left corner during playback. (The animation shows day-time duration, but if one were on the other side of the planet, then it would be the night-time duration.) Another demonstration of this can be seen in the MESSENGER Tribute Video, and observing the rotation of Mercury from 0:59 to 1:15. During this video, pick a spot on Mercury at/near dusk, note the date/time at the top of the video, and follow it around until dawn, then check the date/time at the top of the video again.

So, answering the second question first, assuming that the observation requirement is for NO Sun to be in the sky, it would be possible to observe a given object for upwards of 88 days. However, if the Sun is allowed to be above the horizon to some level, and there was adequate light shielding installed on the telescope, it would be possible to observe a given object for longer than 88 days. Remember that there is no appreciable atmosphere around Mercury to cause scattering of sunlight, so the sky would be dark even when the Sun is above the horizon. (Space telescopes like the Hubble are in perpetual daylight, except when they happen to pass through the Earth's shadow.)

As for the first question, assuming that 'entire universe' simply means 'the entire sky visible from a particular location on the surface of Mercury', then over the course of one Mercury night an astronomer on the planet's equator would have the opportunity to view the entire sky, which again can be demonstrated by the animated graphic in the first link above.

--Mark Kochte, Johns Hopkins University Applied Physics Laboratory
MESSENGER MASCS mission operations team

The January issue of 'Astronomy' magazine (page 50) has an article suggesting there is much less water on Earth's Moon than what was previously thought. Do we have a level of certainty about the water discovered on Mercury by MESSENGER? Could it be said that Mercury has more or less water than the Moon? - submitted by Bryce Johnson, Journalist, 01-22-2014

We can say with strong certainty that Mercury does have a large amount of water. The grounding for this certainty is contained in the diverse sets of data (radar, neutron, temperature via topography, laser reflectance) that all independently show the permanently shaded regions at Mercury's north pole (and by extension its south pole as well) contain nearly 100 wt.% water ice. In contrast, the same types of data at the Moon demonstrate that its permanently shaded regions, on average, are not nearly as enriched in water as those on Mercury. Generally accepted values for the Moon are around 1 wt.% water (or water equivalent hydrogen as measured with neutron data). Even so, there are some indications from space-based radar data that some small craters at the Moon might be more enriched in water. All said, it is fair to say that the permanently shaded regions at Mercury have more water than the Moon; however, this does not mean that the Moon's poles are "dry" per se. Ultimately to find out for sure, one needs to land a spacecraft in a lunar permanently shaded crater and measure the water.

--David Lawrence, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

how many time does mercury spin around the axis? - submitted by destiny williams, Middle school student, 10-29-2013

The concept of a "day" on Mercury is more complicated than we are used to from our experience of living on Earth. See this previous question and answer for more information on the length of time that Mercury takes to spin once on its rotational axis,
and the difference between that and a Mercury solar day.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

relative to our planet, how old is mercury, more or less than 4,5 billions??? thanks.... - submitted by pedro antunes, Interested public, 10-02-2013

The lack of rock samples from Mercury prevents the derivation of a precise age measurement. However, theoretical models of the formation of the terrestrial planets (Mercury, Venus, Earth and Mars) show that they all likely formed in a time scale of about 100 million years or less since "time zero", defined as the formation of the first solids in the proto-planetary nebula. These first solids are estimated to have condensed at about 4.56 billion years ago. Thus, Mercury should have formed about the same time as did Earth, although a precise relative chronology is currently beyond our capabilities.

--Simone Marchi, NASA Lunar Science Institute - Center for Lunar Origin and Evolution

Is it true that the Sun's magnetic field actually protects Mercury from galactic cosmic rays? Is this complete protection or just a reduction in particle intensity? Also, is the protection available all the time, or does it vary over Mercury's orbital period? Thanks again!

- submitted by Bryce Johnson, Journalist, 03-18-2013

Galactic cosmic rays originate from outside of the solar system, and therefore must penetrate the solar magnetic field in order to enter the inner solar system. During solar maximum (the 11-year cycle of increased sunspots and solar activity), the Sun's magnetic field is at its strongest and is most effective at blocking galactic cosmic rays. We are currently (2013) at solar maximum, and therefore the galactic cosmic ray flux at Mercury is lower than normal. However, the galactic cosmic rays have a wide range of energies, and the solar magnetic field is most effective at deflecting the lower-energy particles. Therefore, the protection is incomplete and most cosmic rays still enter the solar system. The protection does vary somewhat as a function of the distance from the Sun, but the range of distances for Mercury's orbit aren't enough to cause this protection to vary on Mercury throughout its year.

--Patrick Peplowski, Johns Hopkins University Applied Physics Laboratory
MESSENGER Geochemistry Discipline Group

HI. Please can you answer to me the following: 1-How much the solar constant at the service of the planet? 2- How much the ambiet pressure at the service of the planet? 3-How much the quantity of ice at the poles of the planet ? why it is not vaporised at nearst distant between mercury & sun? 4- can MESSENGER take photo to the edage of the ice lake at the poles ? Your Sincerely, Ali Shalan Edam Al-kakani. Doctoral Seminer for Earthquake Protection System, IRAQ- BAGHDAD

- submitted by ALI SHALAN EDAM, Other educator, 10-06-2012

1. The solar constant at Earth is about 1360 Watts per square meter. For other distances from the Sun, this scales simply by the inverse-square law. Since Mercury's average distance from the Sun is 0.39 AU, the solar constant at Mercury should be about 1360 x (1.0/(0.39^2)) = 8940 W/m^2.

2. Mercury has a surface-bounded exosphere. Read more about it, including the surface pressure here.

3. Areas of permanent shadow, in impact craters near Mercury's poles, never receive the direct light of the Sun, and hence are extremely cold. This allows any water molecules to stick and remain as ice for long periods of time.

4. Areas of permanent shadow are difficult to image because they lie in eternal darkness. There may be faint illumination from light scattered into the shadow from surrounding crater walls. The MESSENGER camera is collecting some test long-exposure images to determine if any details can be resolved in the areas of permanent shadow. Also, data from the laser altimeter is being analyzed to determine if any differences in surface reflectivity (at the laser wavelength) can be measured in permanent shadow.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist


Mr. X ‏@toktokalweer1ei    Is there any indication Mercury had a moon in the past, or still has on the Lagrangepoint L4 and/or L5? - entered by Q&A admin, 08-29-2012

We have no evidence that there are now or were previously any moons of Mercury. A more comprehensive search for small natural satellites may be made later in the MESSENGER mission.

--Clark Chapman and Bill Merline, Southwest Research Institute
MESSENGER Geology Discipline Group

The display of the change in apparent size of the Sun is neat, but even neater might be a display of the Sun's apparent motion in Mercury's sky. I read many years ago in an essay by Isaac Asimov that on some parts of Mercury the Sun rises, stops, and then sets again before rising and continuing across the sky. Is there such a display or could you make one?

I think when I read this back in the 60's it was known that Mercury has a 59 day rotation period as opposed to the 88 day synchronous rotation thought before, but Asimov may have written the peice before that. It was fascinating. Thank you for the nice video you people have made. - submitted by Jeffrey Kretsch, Interested public, 08-23-2012

An animation showing the Sun rising, stopping, moving backwards slightly, then resuming its motion toward setting is available here, with some more explanation here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What did you make of the description of the appearance of the Sun at dawn on Mercury in the opening chapter of Kim Stanley Robinson's new novel "2312." The description of sunrise on mercury is brilliant writing. I thought from the description that the Sun would appear bigger from Mercury' surface than the "two and a half times the size of the Sun seen from Earth" estimate confirmed in this knowledge base. Now to my two linked questions for you. I understand that at the Earth's equator, dawn travels at about a 1000mph. Is it true that Mercury rotates so slowly that you could walk fast enough across its surface to stay ahead of the dawn? Because of Mercury's strange orbit might dawn stop and go backwards for a while? - submitted by Chris Roberts, Interested public, 07-02-2012

I found a few pages of the novel's Prologue at the website of an on-line book retailer. Mr. Robinson does provide a vivid portrait of sunrise on Mercury. I once saw a total solar eclipse, and it is interesting to think that on an airless body like Mercury, every sunrise or sunset would present the opportunity for an eclipse-like view of the solar corona and prominences.
With regard to the speed of the terminator (line between the day side and the night side), it is easy to calculate that the speed of the terminator at Earth's equator is about 1000 miles per hour. This is because the circumference of the Earth is about 25,000 miles, and the Earth rotates in 24 hours. Mercury rotates on its axis much more slowly, and its orbital path around the Sun is much more elliptical than is the Earth's. These factors and the planet's 3:2 spin-orbit resonance complicate the path of the Sun across Mercury's sky. Indeed, the Sun does stand still in the sky and move backwards for a time, as you can see in this animation:

A "solar day" on Mercury, the period of time from which the position of the Sun in the sky at a given, fixed Mercury longitude returns to that same position is 176 Earth days. Mercury's circumference is (3.14159 x 4880 km). I leave it as an exercise for the reader to compute the average speed of the terminator.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

If I was standing on the surface of Mercury how large would the sun appear to be in the sky compared to its apparent size on earth? - submitted by Scott Leveton, Interested public, 05-07-2012

Good question, one that has been asked before. Take a look here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

What are the comets closing or entering the elliptical path of mercury around the sun between 2012 and 2014? How close will MESSENGER be to the closest one in order to send us a picture or some data to us on Earth? Besides the perihelion shift forward of mercury around the sun, why is it that its aphelion is slightly shifting? Is there any known change of mass pertaining to this effect ?! All feedback is welcomed. Thank you for your lights. Kind regards. - submitted by Hugues CAULIER, Interested public, 04-12-2012

The only comet will come close to Mercury in the next few years is 2P/Encke. There are undoubtedly many of the so-called sungrazing comets that may also come close, but they are often not discovered until they burn up in the Sun. MESSENGER was designed to systematically study the planet and its exosphere, so it is not optimized for comet observations. However, in special cases it may be possible to do so.

The perihelion of Mercury's orbit around the Sun advances because of relativistic effects. The aphelion is 180 degrees away, and moves together with the perihelion. Mercury is constantly gaining small amounts of mass from the addition of material from cosmic bodies (dust, meteoroids, comets, etc.) that collide with the planet, and losing mass by sputtering of surface material into the exosphere. Some mass may also be lost in energetic impacts that eject material at speeds above escape velocity. However these additions and subtractions are tiny in relation to the mass of the planet.

Ron Vervack, Mark Perry, and David Blewett - Johns Hopkins University Applied Physics Laboratory
MESSENGER Science Team

I've just looked at an image of the south pole of Mercury and I see the black areas are the no sunlight areas, but there is a bar of another color that runs across the image which doesn't seem to match how the light would fall on a globe. Is that an artifact of the imaging or does it reveal something about the shape of the planet? - submitted by edward jones, Interested public, 04-05-2012

That bar of color that runs across the 90° E and 270° E longitudes is due to Mercury's unusual 3:2 spin-orbit resonance and the elliptical nature of Mercury's orbit. These longitudes on Mercury, the "cold poles," experience noon at the furthest distance from the Sun and are sunlit for less time during one Mercury solar day than other longitudes. One of the best ways to visualize this effect is to watch these two animations: Mercury's orbit and rotation rate and the motion of the Sun as seen from Mercury's surface. You'll see that days on Mercury are quite different than what we have on the Earth!

--Nancy Chabot, Johns Hopkins University Applied Physics Laboratory
MESSENGER MDIS Instrument Scientist

What is Mercury's impact on the Solar System? If, for instance, there was no Mercury, would our experience of life on Earth be any different? Would conditions in the rest of the Solar System be different? Thank you and best wishes for a successful mission! - submitted by Val Gendleman, Interested public, 03-06-2012

 If Mercury did not exist, there would likely be little effect on the Earth today. There might be some minor sociological difference since religions and astrologers that assign supernatural significance to the planets would have one fewer object in the sky to create stories about. However, it is possible that Mercury played a role in the early Solar System that influenced the formation of the inner planets and thus may have helped to produce the Earth as it is today. MESSENGER has found that Mercury is richer in volatile elements that was previously surmised; hence Mercury may have formed in a position different from the one that it now occupies, or may have incorporated material from a wider "feeding zone" as it grew by accretion. Mercury's importance to humanity is therefore as a storehouse of information on the formation of the planets and as a fascinating oddball object that helps scientists to stretch their ideas and test their hypotheses about how planets operate.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Parrticipating Scientist

How high in the sky does the Sun appear at noon on the equator of Mercury? How high in the sky does the Sun appear at noon at the pole?  Thanks . nicholas. - submitted by Nicholas Roeder, Elementary school student, 02-29-2012

Mercury's rotational axis has near-zero tilt with respect to the plane of its orbit around the Sun. Therefore, at noon on the equator, the Sun would appear directly overhead. Likewise,
at the poles, the Sun would be on the horizon. You might like to look at this animation that shows the motion of the Sun across the sky, for an arbitrary mid-latitude location on Mercury.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How high in the sky does the Sun appear at noon on the equator of Mercury? How high in the sky does the Sun appear at noon at the poles? - submitted by Kate Carniol, Elementary school student, 01-18-2012

A popular question! See the answer here.


Is it at all possible that Mercury is the remnants of a Gas Giant i.e its core? As Mercury is approx the same size as our Earths core? - submitted by Barbara, Interested public, 01-17-2012

If we consider the size of Mercury (a radius of about 2500 km), then it is comparable to the probable size of a gas giant's rocky core (Jupiter's core is thought to have a radius of about 5000 km), however the question is more complicated than that.

The reason why the inner Solar System consists of rocky planets, and the outer Solar System of gas and icy planets is because the different materials that accrete to form the planets are stable at different temperatures. It is not possible at Mercury's current orbit, close to the Sun, for a gas giant to have formed. Dynamical models of the Solar System do predict that the planets have migrated in the past, so could it be that a gas giant formed in the outer reaches of the Solar System and then moved towards the Sun and lost its outer gas layers in the process? This kind of idea has been proposed to explain the Mercury's high density, i.e., much of the rocky (and possibly gas) portions of an early-Mercury were removed (e.g. by evaporation or a giant impact event) to leave a very dense planet with a large fraction of iron metal. Geochemistry results from MESSENGER since it has been in orbit around Mercury, have revealed that the planet's surface has a composition similar to basalts and an ancient rock type called komatiite that we find on Earth. The surface also contains a high abundance of sulfur, which indicates that the material from which Mercury accreted was reduced (in the chemical sense, low in oxygen). If an ancient gas-giant version of Mercury had formed at a greater distance from the Sun and then migrated inwards, the material from which it formed would have been richer in oxygen than is evidenced today. Mercury is also not depleted in volatile elements, which would likely be lost if the planet's outer portions had been removed.

Mercury's surface (like the Moon's) is very ancient, dating back to almost the beginning of the Solar System. Therefore, it seems difficult and unlikely for a gas giant to have formed in the outer Solar System, migrated inwards to Mercury's current orbit, lost its outer gas layers, and then gone through the geologic history that we see recorded on the surface.

-Shoshana Weider, Carnegie Institution of Washington, DC
MESSENGER Geochemistry Discipline Group

What is the actual speed of the terminator over Mercury's surface? Is it true a person could stay ahead of it just by walking? - submitted by Bryce Johnson, Journalist, 01-10-2012

See this answer to a similar question: #qn408


How long does it take a radio signal to be received on Earth from MESSENGER? - submitted by John Swetonic, 11-28-2011

Depending on where Mercury and Earth are in their orbits, the "one-way light time" can vary from about 4 minutes to about 12 minutes.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

hi, i'm a norwegian student, currently working on a small presentation about Mercury, and i was wondering about a couple of things.

1: as far i can understand, the huge temperatur differences from night to day are caused by the lack of a proper atmosphere, but i keep wondering, is there other reasons for the 610 degrees celcius differencial from night to day? and to follow up on this, how quick does the temperature change? - submitted by Truls Finborud, College student, 10-25-2011

On the Earth, the atmosphere acts like a blanket that helps to moderate temperatures between the Sun-lit (day) side of the planet and the night side. On an airless body like Mercury, the surface temperature is determined by radiative equilibrium. That is, the balance between heating of the surface by incident light from the Sun, and emission of thermal infrared
(heat) radiation by the hot surface. As Mercury rotates on its axis, a point on the surface will receive differing amounts of input heating as the Sun moves from rising to setting. After sunset, the surface will cool as thermal emission of infrared carries energy away from the surface.

See this animation to get a better idea of day, night, and temperatures on Mercury.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Congratulations for the mission  and thanks for the communication through this website. Is there evidence of ozone in the atmosphere of Mercury? Is there a greenhouse like on Venus? Thanks. - submitted by Carlos Federico Rovera, Other educator, 09-27-2011

Ozone (O3) has never been observed at Mercury, and it is unlikely to ever be observed because the chemistry necessary to generate it doesn't work in the exosphere. There are traces of ozone on some icy satellites, but that's related to the fact that they are made of ice. Mercury has a totally different (rocky) composition.

The MESSENGER Fast Imaging Plasma Spectrometer (FIPS) has seen good evidence for ionized oxygen (O+). Neutral oxygen may also be present; the Mercury Atmosphere and Surface Composition Spectrometer (MASCS) has searched for it, but neutral O is very difficult to detect.

As for a greenhouse effect, a Venus-like greenhouse requires a substantial atmosphere for the heat-trapping mechanism to work. (The atmosphere of Venus is about 90 times more dense than that of Earth.) Mercury's exosphere is actually a better vacuum than most laboratory vacuum chambers, so the density is far, far too low to initiate a greenhouse. Nonetheless, the tenuous exosphere is very important in telling us what interactions are taking place between Mercury's surface and the space environment!

--Ron Vervack, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I am confused about the time Mercury rotates on its axis. Some places state 176 Earth days, like you state, but several state 58-59 Earth days. I am teaching rotation of different planets and would like to know why there is a disagreement? And which is correct 176 days or 58 days? - submitted by kimberly white, K-12 teacher, 09-20-2011

Mercury spins on its axis once in about 58 Earth days. This is Mercury's "day" with respect to the fixed stars (the sidereal day). But because of Mercury's elliptical orbit, the time it takes for the Sun to reappear at the highest point in the sky is 176 Earth days. That is, the solar day on Mercury is 176 Earth days.

Look at these links for explanations and animations that illustrate the movement of Mercury around the Sun, and the motion of the Sun across Mercury's sky.

How fast does Mercury spin?

How many days in a year?

How long is a day on Mercury?

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Has MESSENGER yet seen any Vulcanoids?.. Thx.. Raj - submitted by Raj Pillai, Interested public, 07-06-2011

Not yet. But then we've given only first looks to many of the images taken more recently. We will be doing a more thorough study to see if any faint vulcanoids escaped our notice. And we hope to keep looking during later phases of the MESSENGER mission.

--Clark Chapman, Southwest Research Institute
MESSENGER Co-Investigator

With great interest I follow the MESSENGER mission. I am a retired molecular biologist and an active astro-imager using a C11 telescope. Together with my astro-friends Willem Kivits (C14 telescope) and Arnaud van Kranenburg (C11) we concentrate on imaging Mercury in the near IR as well as in other spectral regions. During the current apparition we collected a lot of data. I herewith show you an example, a picture obtained by myself and the short movie was made by Willem Kivits all at 680 nm. The latter was made from 10 subsequent images collected within one hour and put together in a movie to demonstrate what is real and what is due to noise. Willem's results and mine show several common albedo features and we try to relate these features with objects on the MESSENGER maps. Unfortunately we discovered that many, even prominent features have not been named yet.
My questions are, is there already a map with more nomenclature than the current one and what kind of system does the MESSENGER team use to refer to certain craters and other features? Are they referred to by their coordinates?
 Our objective is to correlate MESSENGER results to Earth-bound observations. To what extent are amateur results interesting for your team?
With kind regards, Dr. John Sussenbach, the Netherlands - entered by Q&A admin, 06-12-2011

Congratulations on your excellent observing efforts! It is remarkable what can be accomplished with a small telescope in the hands of dedicated observers. You may be familiar with the paper by amateur astronomers Ron Dantowitz, Scott Teare and Marek Kozubal published in the Astronomical Journal in 2000 (vol. 119, pp. 2455-2457). They identified a bright spot on the non-Mariner 10 side of Mercury; this feature was imaged by MESSENGER during its third flyby.

Within the MESSENGER team, we use informal names or latitude/longitude coordinates to refer to features for which the International Astronomical Union has not yet approved names. Team members will be drafting several proposals for feature naming within the coming months. You can keep up with the naming of Mercury features on the I.A.U./U.S. Geological Survey planetary nomenclature page.

Amateur images of Mercury were more interesting to the team prior to MESSENGER's arrival. One area where amateurs might be able to contribute is in photometric observations of Mercury at phase angles that MESSENGER, because of restrictions involving its sun shade, is unable to make.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Two short questions for Mission Ops: 1) On what date will Mercury next reach perihelion? 2) Which meridian will be directly under the Sun at that time, the 0- or 180-degree meridian? Thanks! Bryce Johnson, Rockford, Illinois - submitted by Bryce Johnson, Journalist, 05-16-2011

The next perihelion of Mercury will be on June 12th, 2011 (Day 163). The meridian line that will be under the Sun at that point will be the 180-degree longitudinal line. Due to Mercury's 3:2 spin resonance, the next time Mercury is at perihelion (September 8, or 88 days later) the longitudinal line will be the 0-degree line.

--Mark Kochte, Johns Hopkins University Applied Physics Laboratory
MESSENGER MASCS Mission Operations Lead

How large would the Sun look when viewed from the surface of Mercury? - submitted by Scott L, Interested public, 05-10-2011

On average, Mercury's distance from the Sun is about 39% of the Earth's. At Earth, the Sun covers about 0.5 degrees in the sky. From geometry, this translates to an angle of about 1.3 degrees in Mercury's sky. In other words, if you were standing on the surface of Mercury, the Sun would appear about 2.5 times larger than it does here on Earth.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why was only half of Mercury seen? Can we see the other half? - submitted by Jamarcus Lane, High school student, 05-04-2011

The Mariner 10 spacecraft visited Mercury three times in 1974 and 1975. Because of the period of the spacecraft's orbit around the Sun, it turned out that the same side of Mercury was lit by the Sun during the three flybys. Thus Mariner 10 images only covered about half of the surface.

MESSENGER made three flybys of Mercury in 2008 and 2009. MESSENGER was able to see nearly all of the surface that was in darkness for Mariner 10. Now in a polar orbit around the planet, MESSENGER will obtain several types of global image maps including high resolution, color, and stereo.

You can see the pre-orbit image map of Mercury in Map-A-Planet and also in Google Earth.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I got that at Mercury equator if you moved 160 miles per Earth day you could stay the same relative to the sun. Is there some position in the shade that would be temperature tolerable so one could mine the surface? Alan Dedier, San Rafael, Calif, USA.      PS I'm an EE pushing 62. Maybe my nephew could do it. - entered by Q&A admin, 04-22-2011

Without a thick atmospheric blanket to help moderate temperatures, surfaces in shadow will quickly become very cold. The floors of some impact craters in the polar regions are in permanent shadow, and hence may have temperatures only a few tens of Kelvin above absolute zero. Such ultracold conditions would be very difficult for ordinary mechanical systems. But even at Mercury's poles, any vertical surface that is not in permanent shadow will receive the full brunt of solar radiation - some 10 or 11 times more intense that at Earth's distance. The thermal extremes make design of a Mercury lander very challenging. Still, you should encourage your nephew to pursue a career in a field that can contribute to the exploration of the planets. We do not do these things because they are easy, but because they are hard.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Is there a known radation level, for instance, at the equatorial region during solar exposure? - submitted by mark mcgary, Interested public, 04-15-2011

Because the orbit of Mercury is elliptical, the solar flux varies from 11 times that at Earth (at perihelion) to 4.6 times that at Earth (at aphelion). The Sun's ultraviolet radiation is mostly absorbed by Earth's atmosphere. Since Mercury has no appreciable atmosphere, all of the solar radiation reaches the surface. Cosmic rays are also affected by Earth's atmosphere so that even though cosmic rays penetrate the atmosphere, the energy of a cosmic ray hitting the surface of the Earth is generally less than that hitting the surface of Mercury.

--Rosemary Killen, NASA Goddard Space Flight Center
MESSENGER Participating Scientist

Any chance of finding the "mythical" Vulcanoids of any size..?.. Sometimes wonder why Mercury is so cratered. Regards, Mr. Raj Pillai, Bangalore, India. - entered by Q&A admin, 03-31-2011

We have posted several images related to the search for a population of asteroids that may be orbiting between Mercury and the Sun. Check here, and here, and here.

In addition to optical searches with the camera for vulcanoids existing today, MESSENGER team members are examining the size-frequency distribution of impact craters on Mercury for hints that an extinct population of vulcanoids may have hit the planet in the past.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Could the fact that the core of Mercury is so dense is because it was a larger planet in the past? Maybe a gas giant that got to close to the sun and had most of it's atmosphere burned off? - submitted by Craig, Interested public, 03-30-2011

Compared to the other terrestrial planets, Mercury has a high ratio of metal to rock. One of the hypotheses for Mercury's formation involves the early Sun, which was much hotter and active than it is now. This could have evaporated considerable amounts of Mercury's crust and mantle, leaving behind an iron core covered by a relatively small rocky mantle. This model makes certain predictions for the composition of Mercury's crust and mantle. MESSENGER's geochemical sensors will be making measurements to determine if the actual composition of the planet matches the model predictions.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Current theories suggest that some of the outer planets formed in orbits much closer to the Sun then migrated to their present positions through various encounters and gravitational perturbations. What are the leading theories on where and how Mercury formed and evolved to its present orbit and state? - submitted by Ralph Ricketson, Interested public, 03-25-2011

Dynamically reasonable possibilities for the accretion of the terrestrial planets allow a wide range of outcomes for Mercury.  During runaway growth, Mercury-size bodies can experience substantial migrations of their semi-major axes, according to modeling by the late George Wetherill. Some hypotheses for explaining Mercury's high metal-to-silicate ratio require Mercury to have formed relatively close to the Sun compared to the other planets. For example, the compositional state may have been an outcome of the vaporization of silicates by intense nebular radiation and their removal by a strong solar wind near the early Sun. As MESSENGER gathers more information on Mercury's composition, we will be able to test the various hypotheses for Mercury's formation and evolution.

--Roger Phillips, Southwest Research Institute

MESSENGER Geophysics Group

I'm a bit astonished as to your mention of a day lasting 176 earth day on Mercury . I believed it was 58,6 earth day ! Making 3 rotations during 2 orbit around the 176 eath days . It is on your FAQ on the Mercury mission .

Question from jacques.lawless.


- entered by Q&A admin, 03-04-2011

Thanks for the comment . You are correct that the rotation of the planet once on its axis is just about 59 Earth days. However a "solar day" on Mercury, i.e., the period of time from which the position of the Sun in the sky at a given, fixed Mercury longitude returns to that same position is 176 Earth days. The effect is so noticeable at Mercury precisely because of the 3:2 resonance you mention.

-Ralph McNutt, JHU Applied Physics Lab

MESSENGER Project Scientist

How MESSENGER cruised through the inner Solar System and arrived at Mercury

Hello! Can you tell me what was the exact timing (like the year, month, date, hours, minutes, seconds, and even fractions of a second) that the MESSENGER Probe was launched? What was the exact time the MESSENGER Probe entered Mercury's orbit? I am doing a science project about Mercury and I would like to know about the MESSENGER probe. Thank you! P.S. Can you include a specific time zone so I can use the exact time so I don't mis-interpret the data. Thanks! =) - submitted by A Middle School Student, Middle school student, 04-29-2015

The launch vehicle carrying MESSENGER lifted off at 2:15:56 a.m. EDT on August 3, 2004. The propulsive maneuver (rocket burn) to place the spacecraft into Mercury orbit was begun at 00:45:15 UTC on March 18, 2011. The maneuver was completed at 00:59:58 UTC on March 18, at which time the spacecraft was captured into orbit.

Be sure to check out APL's MESSENGER website for tons of other information about the mission, the spacecraft, and the science of planet Mercury. (including the Mission Timeline.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How long would it take to get to mercury from a moon? - submitted by Isaac, Elementary school student, 01-30-2015

I'm not sure if you mean traveling to Mercury - (A) from a moon of Mercury, or (B) from Earth's moon (that is, "The Moon"). Since Mercury has no moon, option (A) doesn't really apply. As for (B), only two spacecraft have travelled from the Earth-Moon system to Mercury: Mariner 10 and MESSENGER. Mariner 10 was launched on November 3, 1973. It flew past Venus on February 5, 1974 and made its first Mercury flyby on March 29, 1974.
MESSENGER was launched on August 3, 2004. It made an Earth flyby on August 2, 2005, then performed two Venus passes on October 24, 2006 and June 5, 2007. MESSENGER's first Mercury encounter took place on January 14, 2008. This was followed by additional Mercury flybys on October 6, 2008 and September 29, 2009. The spacecraft finally entered Mercury orbit on March 18, 2011.
So why was it only about five months from Mariner 10's launch to its first Mercury flyby, but it took MESSENGER over three years from lift-off to its first Mercury encounter? The reason is that MESSENGER's path was designed to end with the spacecraft entering Mercury orbit. Thus MESSENGER needed to make a much larger change to its velocity than did Mariner 10. MESSENGER used the gravitational encounters with Venus and Mercury to supply the required velocity change.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Good day! I watched the video at here, and I noted that, though the Earth does indeed rotate on its axis during the frame sequences, there is little, if any, indication of cloud movement. What is that? - submitted by Jim K, Interested public, 08-06-2013

The simple answer is that the Earth rotates much faster than clouds move. For example, at the equator, the speed of the Earth's rotation is about 1000 miles per hour. Clouds might move a few tens of miles per hour. In the movie, the diameter of the Earth is
about 200 pixels north to south, so the pixel dimension is about 40 miles per pixel. As the spacecraft recedes from Earth, this pixel dimension increases by a factor of perhaps four or five. Thus the MDIS pixel size is huge compared to any cloud motion in the sequence. In the movie, the longest you can see any particular spot is about 5 hours. In that time, a cloud may move at most a few hundred miles. Thus the cloud motion may be only a pixel or two, or even less than a pixel, depending what part of the sequence we are looking at. Therefore it is not surprising that no cloud motion is perceptible in the movie.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I have no idea why the Messenger choose to flyby Earth without gain more velocity and waste one year. I learned that 1:1 resonant orbit do not provide any benefit when impulse propulsion is used. So why do not launch directly to Venus? - submitted by waloga, College student, 11-14-2012

There are several reasons that the mid-summer 2004 MESSENGER launch opportunity was selected. The primary reason is that NASA's Discovery Program required that MESSENGER launch during 2004. Given the low launch energy, post-launch velocity change (delta-V) available from the spacecraft's propellant load, and flight time limits related to available funding and spacecraft design lifetime, the August 2005 launch opportunity was the next feasible launch opportunity for MESSENGER. However, launch delays past August of 2004 almost certainly would have resulted in cancellation of the mission. Another consideration was that an increase in declination of launch asymptote (launch direction) in August 2005 would have required additional propellant on the launch vehicle (Delta II rocket), thereby requiring a small reduction in propellant loaded onto the spacecraft.
The trajectory brought the spacecraft back past the Earth and Moon in August 2005. This provided the opportunity to obtain images and spectral data with the camera and spectrometer. The data were useful for calibration purposes, and for scientific comparisons of the lunar data with data for Mercury collected later in the mission.

--Jim McAdams, Johns Hopkins University Applied Physics Laboratory
MESSENGER Mission Design Lead Engineer

Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How long did it take MESSENGER to reach Mercury? - submitted by Nathan, High school student, 05-10-2012

Take a look at the MESSENGER website, under Mission Timeline.

Hi There, Can someone on the MESSENGER team tell me about the burn that is required and the subsequent trajectory produced to take MESSENGER out of an Earth parking orbit and into a Sun centred ellipse towards Mercury? I have read that the engine is fired in the opposite direction to the motion of the Earth and the spacecraft continues in the same direction as Earth but achieves escape velocity from Earth. I'm not clear on the direction of the burn in relation to Earth, where that craft is with respect to Earth when this burn occurs the exact trajectory of the orbit once the burn is complete. If there is any material that would help me with this that would be great. Thanks. - submitted by Jeff Stanger, K-12 teacher, 01-21-2012

The spacecraft was launched directly into a heliocentric (Sun centered) orbit and traveled in the same direction around the Sun as the Earth and Mercury do. There is a good description of the launch events in the 2005 paper, "Trajectory design and maneuver strategy for the MESSENGER mission to Mercury" by J. V. McAdams et al. (see page 6), available on the Publications section of the MESSENGER website. Also, you can find several images and descriptions of MESSENGER's heliocentric orbit from launch through Mercury orbit insertion here. The 2011 paper, "MESSENGER – Six primary maneuvers, six planetary flybys, and 6.6 years to Mercury orbit" by J. V. McAdams et al. contains several images of the orbit as well as detailed tables of the maneuvers the spacecraft has performed prior to entering orbit about Mercury beginning on page 8. This paper is also available on the Publications section of the website.

TCM-1 was the first maneuver performed by the spacecraft and its main purpose was to correct launch inaccuracies and adjust the spacecraft's heliocentric orbit so that the timing and location of the Earth Flyby would be correct; the direction of the maneuver was chosen in order to accomplish that. The spacecraft was also 7,677,661 km (0.051 AU) from the Earth when TCM-1 took place on August 24th, 21 days after launch. The thrust direction of the maneuver was 169 deg off of the spacecraft's velocity relative to the Sun, so not exactly opposite to the direction the spacecraft was traveling, but close to opposite. A picture of these vector directions can be found here. You can also see in this picture that the engine has to be pointed in the opposite direction of the thrust (or Delta-V) direction (think of a rocket lift-off: the thrust is pointed up, but the engine is pointed down) . The maneuver was a small one, only changing the spacecraft's velocity by 18 m/s. Compare this velocity change to the first large deep space maneuver that changed the spacecraft's velocity by over 300 m/s or the velocity changes of up 6.9 km/s that were achieved by the planetary flybys (see Table 5, column 1 of the second paper mentioned above). There is more information on the maneuvers and flybys on the mission design section of the website.

-Dawn Moessner, Johns Hopkins University Applied Physics Laboratory
MESSENGER Mission Design team

How do you determine where in space a space craft is while flying toward its destination?

I can see a couple of options:

A) Optically looking at the craft in a telescope and compare its location to other known objects (stars, sun and planets).

B) Sending out a laser beam towards the craft and see when the beam reaches the craft, bounces off it and returns to Earth (sort of an optical radar). I think this has been done to very precisely determine the distance to the Moon, but I can see problems with this method as the distance to the craft is increasing.

C) Instead of a laser, you could send a radio command to the craft and ask it to return a signal as quickly as possible and you get at least the distance to the craft, but not its location.

D) Having more than one radio receiver on Earth and detecting the difference in the signal arrival time from the craft (I think this is called triangulation?).

E) For better accuracy when the craft is in orbit around a remote planet, the craft might itself determine its position relative to Mercury (at least altitude from the Mercury surface) with maybe a 'laser type radar' (as mentioned above).

F) Maybe the craft can observe objects (optically) around itself (sun, stars, planets) and calculate where it is? I think this was done with one of the European missions out to Saturn, right?

Is any of this correct? Maybe use a combination? Are there other techniques? - submitted by Andy, Interested public, 05-05-2011

You have given the problem some serious thought, and have hit on some good possible solutions.

The spacecraft uses its star-tracker cameras to measure its orientation in space. The velocity and location are determined from Doppler tracking of the spacecraft's radio signal.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

First of all, congratulations on a successful insertion burn! After the trip to safe mode during the 3rd flyby I was biting my nails for this one. I was glad to hear that you disabled a lot of the protections for the burn.

A] I have a question about the insertion burn. In watching the graphic, I noticed that the spacecraft did not maintain a fixed inertial attitude during the burn. It apparently kept the thrust aligned with its instantaneous velocity vector as it curved around
Mercury. Is this right, and if so, why? Is this more fuel-efficient than maintaining an inertially fixed thrust vector that coincides with the velocity vector at periapsis? How much difference does it make?

B] I dabble in astrodynamics from time to time and I've even applied some of it to amateur radio satellites, but the interplanetary billiards game you guys played with MESSENGER was just jaw-dropping. I can propagate a state vector given all the forces on a spacecraft so I could probably confirm that a particular series of flybys and maneuvers would get you to Mercury -- but how did you work it all out in the first place?! Are there any general design principles or approaches you can use to plan an interplanetary mission to whittle down all the degrees of freedom? Do you simply enumerate every possible planetary flyby sequence and then work each one, varying Earth departure times, inserting deep space maneuvers, etc, to see if it's possible to get to your destination with reasonable delta-V? Or what?       Thanks, Phil Karn - entered by Q&A admin, 04-22-2011

A) The MESSENGER orbit insertion maneuver was optimized to use the minimum amount of propellant, with only one minor exception in that the maneuver start time was chosen to place the MESSENGER spacecraft > 30 degrees above the horizon relative to antennas at Goldstone, California and Canberra, Australia. The instantaneous thrust vector direction was offset by as much as 4 degrees from the instantaneous direction opposite the spacecraft velocity, because the Mercury orbit insertion maneuver was used to rotate the line of apsides (the long axis of the ellipse-shaped orbit) by 6 to 7 degrees northward. Using fixed-thrust-direction for the almost 15-minute duration orbit insertion would have not been possible given that the higher velocity change with the fixed-direction maneuver would have likely depleted all usable oxidizer before maneuver completion. Oxidizer is mixed with fuel to obtain the highest efficiency, highest thrust, bi-propellant portion of orbit insertion.

B) The principles behind the trajectory design of MESSENGER's heliocentric orbit were first published by Chen-wan Yen of NASA-JPL in 1985. Chen-wan worked with MESSENGER Mission Design Lead Jim McAdams from 1998 to 2002 to help identify the primary and back-up launch options for heliocentric trajectories to Mercury. The trajectory used by MESSENGER was the third and final combination of launch date, planetary flybys, and course-correction maneuvers available for launch in 2004. The Earth flyby allowed a launch date one year earlier than August 2005, and the third Mercury flyby and subsequent deep-space maneuver was needed to lower the propellant required for Mercury orbit insertion. The design method for these types of interplanetary trajectories is documented and repeatable, although it is complex and requires expertise and highly qualified software.

--Jim McAdams, Johns Hopkins University Applied Physics Laboratory
MESSENGER Mission Design Lead

How was MESSENGER inserted into the orbit of Mercury? Mercury has only 1/3 the gravitational pull of the earth, why it was not attracted to the Sun? - submitted by xyz, College student, 04-09-2011

Here is an answer that may help. Also, read more about orbit insertion and the reasons for MESSENGER's long path to Mercury.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Approximately how long will it take the MESSENGER probe to get to Mercury? - submitted by Kathy Gallo, Middle school student, 04-03-2011

MESSENGER was launched on August 3, 2004 and entered Mercury orbit on March 18, 2011.



Hey, I am a Grade 12 high school student, and I am doing a project on Gravity Assists. I would like to know the velocities of MESSENGER and how each flyby impacted the velocity. Thank you. - submitted by Neel Patel, High school student, 04-02-2011

You can read about MESSENGER's planetary flyby gravity assists here.


Why does MESSENGER have to pass by Earth, Venus, Mercury several times before entering Mecury's orbit? What is a 'gravity assist' and why was it impotant to MESSENGER? - submitted by Eloho Eloho, Interested public, 03-30-2011

Answers to these questions can be found in the here.


Hi Margaret, There are answers to very similar questions under the Getting There category of our Q&A page.

I read in the article that MESSENGER traveled 4.9 billion miles. Why so many miles if Mercury is 100 million miles from Earth?  I'm curious about the flight path of MESSENGER to help me understand why the spacecraft had to travel such a long journey. - submitted by Jerry, Interested public, 03-20-2011

MESSENGER's path from Earth to Mercury was dictated by the realities of orbital dynamics and the capabilities of the spacecraft's rocket engine. Unlike science fiction starships that use "warp drive" to fly directly from one place to another, MESSENGER used gravity assists from five planetary flybys to help shape its trajectory to prepare for orbit insertion. This process took about 6.5 years, during which MESSENGER made nearly 16 passes around the Sun. To learn more, watch this animation of MESSENGER's interplanetary cruise, and check out our Mission Design page.

--David Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

I've tried to find the answer on my own, but no luck so far, thus my question. Thankfully it is a moot question now since MESSENGER has successfully entered orbit around Mercury, but I am still curious. Had the Mercury orbit insertion failed to occur due to some transient, correctable condition, was there a contingency plan to allow for another orbital insertion attempt after what would then have been a fourth flyby a few days ago? In other words, could you have "gone around again" for an additional, future insertion attempt? If so, is there a document published somewhere on the WWW describing what this would have entailed? - submitted by John Graves, Interested public, 03-20-2011

MESSENGER's mission design team examined a range of contingency options for recovering MESSENGER's science mission if the orbit insertion burn were aborted or if the burn ran to less than 70% completion. The options, which depend strongly on whether a partial burn occurred and its specific outcome, are described in a paper published in 2010 by David Dunham, Jim McAdams, Dawn Moessner, and David Otteson. The paper is available as a pdf file on the MESSENGER Team Publications web page. If the Mercury orbit insertion burn ran to more than 70% completion, then MESSENGER would now be in orbit about Mercury but not in the desired orbit, and one or more additional maneuvers would have been needed before the onset of mapping.

--Sean Solomon, Carnegie Institution of Washington

MESSENGER Principal Investigator

First ... WOW ... well done.

Is there somewhere I can see the actual flight path of the spacecraft from launch to insertion? I understand MESSENGER "flew by" Earth once and, apparently past Mercury a few times before you got it nestled into its orbit. There's some people out here interested in just what that all looked like. - submitted by John Gillmore, Interested public, 03-18-2011

Indeed, MESSENGER flew past Earth once, and performed gravity assist maneuvers at Venus (twice) and Mercury (three times) in order to get set up for entry into orbit about Mercury. Read more about the launch and cruise phases of the mission at our Mission Design page.

How has MESSENGER traveled over 52 Astronomical Units (March 18, 2011) when there is only 1 AU between the Earth and the Sun? I think the Earth itself only traveled about 40 AU in the same amount of time. How many times has MESSENGER circled the Sun? - submitted by Kevin, Interested public, 03-18-2011

MESSENGER's path from Earth to Mercury was dictated by the realities of orbital dynamics and the capabilities of the spacecraft's rocket engine. Unlike science fiction starships that use "warp drive" to fly directly from one place to another, MESSENGER used gravity assists from five planetary flybys to help shape its trajectory to prepare for orbit insertion. This process took about 6.5 years, during which MESSENGER made nearly 16 passes around the Sun. To learn more, watch this animation of MESSENGER's interplanetary cruise, and check out our Mission Design page.

--David Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

In the FAQ one can read that the complex route of MESSENGER was necessary to decrease its speed to enter the Mercury orbit.

But on every Mercury flyby, the speed increased significantly, and when entering the orbit, the speed was even higher, why is that? - submitted by Axel, High school student, 03-18-2011

The MESSENGER spacecraft used gravity-assist flybys of Venus and Mercury in order to catch up to Mercury, the fastest planet around our Sun. As speed relative to the Sun increases, speed relative to Mercury decreases. Slowing down relative to Mercury can be confusing since the gravitational pull of Mercury is temporarily increasing the spacecraft's speed relative to Mercury as the spacecraft comes within about 200,000 kilometers of Mercury. Just as a slow rolling magnetic ball speeds up as it comes near another magnetic ball, so MESSENGER is pulled by Mercury's gravity to a faster speed for a short time near Mercury. The effect on the spacecraft's orbit from each Mercury gravity assist is such that the spacecraft flies by Mercury at a slower speed for the next Mercury flyby. By the fourth Mercury encounter, the spacecraft has enough propellant to slow the spacecraft enough to transition from an orbit around the Sun to an orbit around Mercury.

Jim McAdams, Johns Hopkins University Applied Physics Laboratory
MESSENGER Mission Design Lead Engineer

The Primary Mission orbit, and what might happen afterward

First, congratulations for such a tremendous achievement, starting with inserting the spacecraft into such an orbit after such a complicated trajectory and ending probably quite a long time in the future after analyzing all the wealth of data it returned. But the question has to do with the fact that, about 30 minutes after the time of impact, I was glancing at the DSN Now page again and noticed that it was saying data was again being received from MESSENGER. Lasted a few minutes, with some pauses, so at the time I was wondering whether it may have somehow skirted just above the surface instead of impacting and emerged on the other side possibly out of control or even damaged because of it, and therefore unable to point the right way for constant communication.Not a conspiracy theorist, mind you (quite the contrary usually), and the news release makes it quite clear that it must have been some sort of glitch on the DSN Now site, but the moment did confuse me at the time and it'd still be interesting to know exactly what sort of glitch and how often it tends to happen, thinking of how it can affect what's shown about other missions as well.Thank you for your time. - submitted by Robert Negut, Interested public, 04-30-2015

We cannot speak to the DSN Now page and how they populate or animate it. There may be a point-of-contact that could address your question.

But in terms of MESSENGER and official communications, the DSN was "listening" for signals for a period during which the spacecraft would have re-emerged from behind Mercury and into view of the Earth had impact not occurred. There were no received signals observed by us or the radio science team at the DSN (we both looked repeatedly from 19:38 to 19:45 until we made the official call that impact had taken place at 19:26 UTC spacecraft time (19:34 UTC at the ground).
If you look at the graph of predicted altitude above the terrain, you can see that MESSENGER's trajectory would have carried it to a close-approach point of about 1 kilometer below the surface. The vertical uncertainty in the plot is a few tens of meters. So it was extremely unlikely that the spacecraft could have avoided impact on that last orbit and come around for one more pass. And moving at a speed of over 8,700 miles per hour, even a tiny brush with the surface would be catastrophic. As can be seen from the graph, the spacecraft struck a small ridge.

--Andy Calloway (MESSENGER Mission Operations Manager) and Dave Blewett (MESSENGER Participating Scientist)
Johns Hopkins University Applied Physics Laboratory

did messenger take pictures while it was falling into mercury?do you have a web page link to those pictures? - submitted by den, College student, 04-30-2015

The spacecraft usually downlinks data to Earth when it is at the point in its orbit farthest from the surface (see this graphic to get an idea of the highly elliptical shape of the orbit). Of course, the impact will occur during the part of the orbit that is closest to the surface (when this distance goes to zero). The spacecraft's orientation favorable for observing the surface may differ from the orientation that is needed to transmit data to Earth. Also, the impact point will be on the side of Mercury that is facing away from Earth at the time of the impact, so signals were eclipsed when the spacecraft passed behind Mercury as seen from Earth.

For these reasons, there are no images of the "death dive". However, our image Gallery has been posting images that were obtained in the late stages of the mission, including ones from the day of the impact.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why is the orbit of Messenger going down?Is it because of friction with the atmosphere? - submitted by Elto Desukane, College instructor, 04-29-2015

Mercury's exosphere is extremely thin, far too thin to affect the spacecraft's motion. See this previous Q&A for an explanation of the orbit's decay.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Dear Sir, i'm interested about the impact, and here are some questions:1.I read that Messenger would hit on the opposite side of Mercury, if not so, how could you see the crash? 2.Reports said that researchers would watch the hole hit by Messenger to study about the process of space weathering, while another report said that " it is uncertain whether a future orbital mission that obtains high-resolution images would be able to tell which crater was formed by the MESSENGER impact", could you tell me something about that?3. In your opinion, dose Messenger feel like a friend who communicate with you everyday? Will you say goodbye to it after the impact? Do you feel sad? Will you miss it?Thanks. - submitted by Coby Wang, College student, 04-24-2015

1. You are correct that the expected impact location will be facing away from Earth at the time of the impact. Therefore, radio communications with the spacecraft are not possible in the minutes leading up to the end.
2. It will certainly be of interest for researchers in the future to try to locate the crater formed by the impact of MESSENGER. Because the exact date of the impact is known, analysis of the crater's color properties in relation to those of other craters could provide clues to the nature and rate at which "space weathering" affects Mercury's surface. Space weathering refers to the physical, optical and chemical changes that take place when rocks and soils on the surface of an airless body are exposed to the space environment: micrometeoroid impacts, bombardment by charged particles from the solar wind or a planetary magnetosphere, cosmic rays, solar ultraviolet light, and so forth.
The challenge will be to figure out which crater is the one made by the spacecraft. It is estimated that the crater will have a diameter of about 16 meters. In order to clearly see a 16-meter crater, it is necessary to have images with spatial resolution about 3 or 5 times smaller. In other words, there need to be about 3 or 5 pixels across a feature so that it can be confidently discerned. That means that images with pixel dimensions in the range of (16/3 = about 5) to (16/5 = about 3) meters per pixel are required. MESSENGER obtained extremely limited coverage at resolutions better than 5 meters per pixel. For example, global coverage with the monochrome map is at 250 meters per pixel - far too coarse to see a 16-meter crater. Thus, even if a future mission obtained images of the landing site at very high resolution, there are no "before" images from MESSENGER with which to make a comparison.
As you can read in this previous Q&A, the Lunar Reconnaissance Orbiter (LRO) spacecraft was able to identify small craters made by some recent spacecraft impacts because both "before" and "after" images at high spatial resolution were obtained.

3. It is a tremendous priviledge to be a member of the MESSENGER science team. I have been among the first humans to see new images of Mercury's awesome landscape, and have been a part of some amazing discoveries. It will be hard to believe that the spacecraft will no longer be sending back new data after April 30, 2015. I think I will have a feeling of loss and sadness. The of scientists who analyze the data and the engineers who make it possible are a fantastic group, and I will miss seeing them when the final team meeting takes place. But I look forward to continuing to work with MESSENGER data and my MESSENGER science colleagues for many years to come.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Dear Sir,Please could you tell me what, if any, preparations have been made to orient MESSENGER for its final descent to the surface of Mercury to ensure data are transmitted until the last possible moment.Has any preparation gone into orienting the craft for maximum survival of impact on the (very unlikely) event of it being able to transmit after landing (for example, to arrange that the antennas are protected as much as possible from the impact) or will landing be too unpredictable?Thank you.Les. - submitted by Les Cross, Interested public, 04-10-2015

A summary of information about the end of MESSENGER's orbital operations around Mercury can be found from a link on APL's MESSENGER webpage ( ../About/Mission-Design.html#final-extended-mission).

At the expected time of impact (just before midnight Eastern time, April 30, 2015), the impact location is not visible to Earth. A description of the series of orbital correction maneuvers during March and April 2015 used to raise the spacecraft's altitude, along with illustrations of the position of Earth and Mercury with respect to the Sun at the predicted time of impact, is shown here.
MESSENGER will be traveling at 3.9 kilometers per second (8,700 miles per hour) when it strikes the surface. The twin GRAIL spacecraft were moving at about 1.6 km/s when they hit the Moon in late 2012. The GRAIL impact sites were photographed by the Lunar Reconnaissance Orbiter, revealing craters about 5 meters (16 feet) in diameter. Scaling relationships suggest that the crater made by MESSENGER will be about 16 meters (52 feet) across. MESSENGER image coverage of Mercury at spatial resolutions sufficiently high to recognize 16-meter craters is very limited, therefore it is uncertain whether a future orbital mission that obtains high-resolution images would be able to tell which crater was formed by the MESSENGER impact.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Greetings! I have two questions. 1: Has MESSENGER spent any of her time looking for Vulcanoid Asteriods? 2: Do you have a date for her End of Mission impact into Mercury? Thanks! Bradley R Waller, St Louis Astronomical Society - submitted by Bradley R Waller, Interested public, 03-19-2015

1 - Vulcanoids have been the subject of several previous questions. Go to the Q&A website and type Vulcanoid in the little search box in the upper right corner to see the responses.
2 - As described in several recent news releases (here and here), the current "hover campaign" should keep MESSENGER at altitudes above zero until April 30, 2015.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why is MESSENGER going to crash into Mercury? If its in orbit, and there's no atmosphere slowing it down, then what is the cause for the spacecraft to lose altitude? - submitted by Skip, Interested public, 02-12-2015

The orbit of a spacecraft around a planetary body is not necessarily stable against perturbations by the body's "lumpy" gravitational field, or by the gravitational influence of other bodies. In the case of MESSENGER's orbit around Mercury, it is tugging by the Sun that causes the orbit to change. Check out the "Orbiting Mercury" section of the MESSENGER Q&A website to learn more, especially the answer to this question.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I've heard that the MESSENGER team is planning on shutting down the space probe in March of 2015 and that you're currently doing maneuvers to ensure it doesn't smack into Mercury before you want it to. Why, especially in the case of MESSENGER, do space agencies power down spacecraft long before they are dysfunctional? I figure it's because it costs so much to keep them up or because a lack of propellant prevents the spacecraft from maneuvering (even so, it could still provide plenty of valuable data). If funding for the program was taken out of the equation, how long could MESSENGER's systems theoretically last? If MESSENGER's mission was further extended what new information could we hope to discover? Lastly, after power down next spring, how long will it take for MESSENGER to crash into the tiny planet below, and if BepiColombo discovers the crash-site a few years from now could we learn anything from the wreckage that will help a future landing mission? - submitted by Suzuki, High school student, 11-10-2014

The rumors you have heard are not quite correct. The MESSENGER mission will indeed come to an end some time around late March of 2015. Based on a comprehensive review after MESSENGER's one-Earth-year primary mission, NASA approved funding for an extended mission. The end-date of the extended mission is dictated by the amount of propellant in the fuel tanks. Because of gravitational perturbations by the Sun, the orbit of the spacecraft around Mercury is constantly drifting toward lower periapse (altitude of closest approach) above Mercury's surface. The spacecraft occasionally performs "orbital correction maneuvers" using its main engine to boost the periapse back up to avoid hitting the surface. But, once the propellant has all been used, there is no way to avoid the inevitable: the closest approach altitude will decrease until it reaches zero, and the spacecraft will crash on the surface.
The crash sites of spacecraft on planetary surfaces are of interest both to the general public (the "wow, that's cool" factor), and to scientists interested in the mechanics of impact cratering. In the case of the Moon, the orbiting Lunar Reconnaissance Orbiter (LRO) spacecraft was able to capture "before" and "after" pictures of the site where the LADEE spacecraft and the twin GRAIL probes hit the surface. LRO is in a great position to do this because it is in a relatively low-altitude, nearly circular orbit and its cameras are designed to capture very high resolution images of the lunar surface.

In the case of MESSENGER and Mercury, things aren't so easy. MESSENGER's highly elliptical orbit prevents it from covering the entire surface at the highest spatial resolution. The camera team has been attempting to obtain high-resolution images of the expected crash site, however the crash location is not known precisely, and various constraints prevent the entire potential crash region from being imaged at high resolution. However, it is possible that, if we are lucky, one of these images will serve as the "before" view of the surface that can then be compared with an "after" view to be obtained by BepiColombo and a tiny new crater will be recognized as MESSENGER's final resting place.

You can read more about the end of the mission in the "Orbiting Mercury" section of the project's Question and Answer website.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How long did Messenger orbit Mercury? - submitted by Jacob, 05-08-2014

MESSENGER entered orbit around Mercury in March of 2011. The primary mission was for one Earth year, until March of 2012. NASA approved funding for an extended mission through March 2013. Today (May 2014), the Johns Hopkins University Applied Physics Lab (APL) continues to operate the spacecraft in the second extended mission. The second extended mission will end in late March of 2015 when the spacecraft will have expended all of its fuel and collide with the the surface of the planet. You can look at the "Where is MESSENGER" feature on the project's website to see the current location of the spacecraft.

--Dave Blewett, Johns Hopkins Applied Physics Laboratory
MESSENGER Participating Scientist

Can MESSENGER transmit data live and the final descent to the surface be recorded ? Andrew Brown, Kent, UK. - entered by Q&A admin, 04-11-2014

"Final descent to the surface" is a nice way to describe a terrifying high-speed crash. There are a number of uncertainties involved in MESSENGER's final orbits around Mercury, which will take place in March of 2015. The ability to return late-stage data depends on the availability of Deep Space Network coverage to receive transmissions, and the amount of data stored on the recorder that needs to be downlinked to Earth. The science and operations teams are beginning to think about these issues. Because of imperfect knowledge of Mercury's gravitational field, and due to the specifics of the topography of the particular part of the planet over which the spacecraft is flying at closest approach (periapsis), it is likely that the actual crash time and location will be unsure within a few orbits. Hopefully plenty of Deep Space Network 70-m antenna time will be allocated to receive downlink from MESSENGER, so that the maximum amount of data can be returned. We want the mission to end a minimum of data left on the recorder.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Would it be possible to image the Rachmaninoff pyroclastic vent/deposit using both MDIS cameras & using MASCS either at or just after sunrise, when the surface is still cryonically cold (approx minus 186 Celsius / minus 303 Fahrenheit or 87 Kelvin) after the long night to see if there are any 'frost' deposits from possible outgassing from the pit freezing out before the Sun burns it off?  Andrew Brown, Kent, UK. - entered by Q&A admin, 04-11-2014

One of the objectives during our extended mission has been to attempt observations of "mini-exospheres" that might be present over some of the various geologic features such as hollows and pyroclastic deposits. The idea is that any potentially volatile material might be concentrated over such regions and exhibit an enhancement in our spectra. That might seem easy enough, but there are a number of complicating issues. First off, the spacecraft has significant pointing constraints due to both keeping the Sun on the correct side of the sunshade and protecting vital spacecraft and instrument components from being heated too much by the planet's dayside surface. You could say we really are between a rock and a hard place, or perhaps between a hot and a hotter place. This limits when and where we can make such observations. Those times are further restricted by the lockstep between the orbit and the particular surface features close to the orbit; i.e., we aren't necessarily in the right place at the right time to make a particular measurement, and that doesn't change much over the lifetime of the mission. Another factor is that we have to be really close to the feature and need to observe at low altitudes. As fast as MESSENGER is moving when we are close to the planet, there is very little time to make an observation. The attempts thus far have been on the order of a minute long. That's not a lot of time to get a measurement in unless the signal from any mini-exosphere is strong. Thus far, we haven't seen such a signal, but the best opportunities are actually still to come, so stay tuned.

--Ron Vervack, Johns Hopkins University Applied Physics Laboratory
MESSENGER atmosphere and magnetosphere discipline group

How are the preparations of MESSENGER's eventual descent coming along. I understand later this year, that periherm will be down to about 25 km ? Is it determined where this low periherm will be occurring ?

Is there new information on the heart shaped volcano located at 22.5° North. 146.1° East, just inside the south west Caloris Basin rim, and the altitude of the mound it's on ? How does this feature relate to the others along the southern Caloris Basin ? I hope both volcanic vents at 36.10 degrees North & 64.80 degrees East and 22.5° North. 146.1° East, will be seen at very high resolutions as well as many of Mercury's other volcanic and other interesting geological features will be seen during this period.  --Andrew Brown, Kent, UK. - entered by Q&A admin, 04-10-2014

Presently (April 2014), MESSENGER's periapsis altitude is a bit below 250 km, and the periapsis latitude is at about 70° N. Indeed, throughout 2014 the periapsis altitude will be drifting lower, with several orbital correction maneuvers to boost it back up and delay impact. Later this year the altitude will twice reach about 25 km. At that time, the latitude of the periapsis will be about 60° N. There are many challenges associated with operations at such low altitudes. For example, during periapsis, the velocity of the spacecraft's motion over the surface is extremely high, such that image smear becomes a problem. The team is presently evaluating combinations of short exposure time, image binning, and compression to determine the best parameters for imaging during these fast flybys. The thermal load from being so close to the hot surface of the planet may impose restrictions that preclude certain science operations at low altitude.
The large volcanic vent in southwest Caloris (near 22.5° North, 146.1° East) is an amazing feature. Besides being covered by the various MDIS imaging campaigns (monochrome morphology, eight-color, stereo, etc.), it has been targeted for special high-resolution images. A quick look at topographic profiles across the feature indicates that the mound is fairly low, a few hundred meters or less. The large vent near 36.1° N, 64.8° E is northeast of the Rachmaninoff basin. It too has been targeted for special observations. A number of targeted observations are already on the ground.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Twitter question: "How close can you get to the surface without gravity pulling you down to the ground?" - entered by Q&A admin, 02-10-2014

Presently, the lowest point (periapsis) in MESSENGER's orbit is about 300 km (190 mi.) above Mercury's surface. Because of the perturbing effects of the Sun's gravity, the closest approach altitude will drift lower, until it reaches about 115 km (71 mi.) in June of 2014. At that point, an orbital correction maneuver (OCM, aka rocket burn) is scheduled; this will boost the periapsis up to about 161 km (100 mi.). Then the periapsis will drift down to quite a low altitude, about 25 km (16 mi.) and again be boosted by an OCM. Before the mission ends in March of 2015, there will be two additional "drift down/boost back up" sequences. During the final OCM, all the propellant in the fuel tanks will have been expended, and the Sun's gravity will inexorably cause the spacecraft periapsis to move closer to the planet's surface with each orbit. Eventually, in late March 2015, the periapsis altitude will reach zero, meaning that the orbital path will intersect the surface - i.e., the spacecraft will crash onto the surface.
You can read more about MESSENGER's orbit and the endgame by browsing the MESSENGER Q&A, on the topic of "Orbiting Mercury".

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Just wanted to know if Messenger is still being funded and for how long. Maybe missed information but will the mission finally end if/when there is an orbital decay (will it eventually crash on Mercury? The mission seems to be going very well and is a great success. Thoroughly enjoyed whole program so far and found it utterly amazing that we can accomplish something like this.Thanks for the great work you guys do!! - submitted by Dan, Interested public, 08-02-2013

Although the proposal for a MESSENGER second extended mission (to March 2015) has not yet been formally approved, NASA has directed that the project be operated in accordance with the submitted second extended mission plan. Funding for operations is on a sort of month-to-month basis. Check out prior questions for discussion of the end of the mission, under the topic "Orbiting Mercury".

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Good Afternoon to ALL at the MESSENGER team. I have been on here several times already. This is not so much a question rather some comments all positive. Love the way that you are now doing many more targetted high resolution observations with the MDIS NAC, bootsing the number of very high resolution views that we have become used to with the Moon & Mars.
- submitted by Andrew R Brown., Interested public, 05-25-2013

Thanks for the supportive words, Andrew. MESSENGER has brought about a quantum leap in knowledge of the innermost planet, and a second extended mission would continue to build on that success.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Has anyone considered what to name the impact crater left by the spacecraft? Have there been any predictions as to the location of this impact point? - submitted by Michael Clyde, Interested public, 05-05-2013

It is unlikely that a future mission would be able to locate the small crater created by MESSENGER's impact, because it will be below the resolution of most MESSENGER images, and because it will be difficult to exactly predict the location of the impact point. See this previous question, and browse the "Orbiting Mercury" section of the Q&A for more about MESSENGER's orbit and what might happen at the end of the mission.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Near the end of the next extended mission, there is mention of going into a lower orbit. How low can you go? The resolution would be fantastic, though the heating from Mercury could be a problem. When all is said and done at the end, could you crash Messenger onto Mercury, taking pictures going down? Thanks!

- submitted by ed_turco, Other educator, 03-21-2013

The mission plan for the proposed Second Extended Mission includes several periods during which the periapsis drifts to altitudes below about 200 km before being boosted back up. There could be time spent with periapsis altitudes considerably lower than 200 km. There are thermal constraints at these low altitudes, because the spacecraft is passing so close to the hot planet. Also, at low altitudes the speed of the spacecraft over the surface is very high, and smearing of images becomes a problem even for the shortest exposure times. Once all the propellant is consumed, the periapsis altitude will drift toward a height of zero, upon which a crash will occur. The latest that the crash will happen is March 2015. In order to return data to Earth, there must be a favorable configuration of the spacecraft, Mercury, the Sun and the Earth. The ability to return data will be an important consideration in planning the final mission end-game.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

In OCM-7 maneuever MESSENGER was used all remaining oxidizer. How much propellant remaining for RCS thrusters? Are there any planned orbit maintenance maneuvers during second extended mission? - submitted by Kamil Rzeszowski, College student, 03-19-2013

Orbital correction maneuvers (OCMs) 7 and 8 were used to change the orbit from a 12-hour period in the Primary Mission to the 8-hour period of the first Extended Mission. At the end of the first Extended Mission on March 17, 2013, the periapsis altitude was
approximately 440 km. Gravitational perturbations from the Sun cause the periapsis altitude to drift lower, and without intervention the spacecraft's orbit will eventually intersect the planet's surface (that is, it will crash). In the plan for a two-year second Extended Mission submitted by the MESSENGER project to NASA Headquarters in early March, 2013, the mission design calls for several additional OCMs when the periapsis drifts below about 200 km. These OCMs will consume the majority of the remaining propellant. The latest date to which impact can be postponed is about March of 2015.

--Dave Blewett
Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Can the mission be extended beyond March 2013? How long can the mission run, in theory? How will the mission end? - submitted by Hal Yngve, Interested public, 02-23-2013

Several recent inquires have asked about the second Extended Mission. Look here and here. Concerning end-of-mission scenarios, browse through the questions here.

--David Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Dear all, is there any chance of MESSENGER imaging comets PANSTARRS (March 2013) & ISON (November 2013 - January 2014) assuming second mission extention is approved? If I remember correctly, Comet ISON will approach Mercury at a far closer distance than to Earth? Perhaps using both NAC & WAC cameras on MDIS. I have suggested that Mars Science Laboratory Curiosity & MER B Opportunity do likewise from the surface of Mars & MRO HiRISE from Mars orbit. Will be glad to hear of any mission extention news from April. Andrew R Brown. - submitted by Andrew R Brown., Interested public, 02-17-2013

MESSENGER will observe both comet ISON and comet 2P/Encke if the second extended mission is approved. We will be able to take both images and spectra. Comet PanSTARRS is not well placed for observations by MESSENGER. MRO will almost certainly try to observe ISON as it passes closer to Mars than to Earth or Mercury.

--Ron Vervack, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

What are your chances for getting another mission extension until 2015? Thanks. - submitted by Jesús, Interested public, 01-04-2013

MESSENGER's present extended mission will draw to a close in March of this year (2013). NASA has asked the MESSENGER project to submit a proposal describing the science goals, engineering constraints and the budget needed for a second extended mission. The proposal is currently in preparation. We are hopeful that NASA will favorably evaluate the proposal and continue MESSENGER's wonderful mission of exploration.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

About this question, I think the messenger name is very well chosen. The spacecraft is far away from us in a very hostile environment. The possibility to communicate and control the spacecraft only puts merit in the team who makes part of this mission. My question is if this mission could be extended a second time, because it's returning useful information, discovering new subjects and also could deliver new exciting knowledge in the future. - submitted by Sergio Silva, Interested public, 12-18-2012

Indeed, MESSENGER's (first) Extended Mission ends in March of 2013. The MESSENGER project is in the process of preparing a proposal to be submitted to NASA for a second Extended Mission. Because of the limited fuel available on the spacecraft to maintain the orbit, the absolute longest that the mission could last is March of 2015. The choice of end-date will be made based on an assessment of the science observations that can be obtained, the thermal environment to which the spacecraft will be subjected in a very low altitude orbit near the end of the mission, and other considerations such as the positions of the Sun, Mercury, and Earth (because this affects the ability to downlink data from the spacecraft to Earth).

Thanks for your interest in MESSENGER's mission of exploration at the innermost planet.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

HI...How much the speed of Messenger with relative to the plant mercury surface? Also with relative to the plant earth surface? Possible to take close photo to the sun surface ? how much the compaction of mercury surface at poles area? Thank you very much. - submitted by ALI SHALAN EDAM, Other educator, 10-18-2012

The orbital parameters for the 12-hour Primary Mission orbit are presented in a table. The speed between the spacecraft and Earth is essentially the speed between
the Earth and Mercury. See a previous question about MESSENGER and observations of the Sun. If by "compaction of the surface at the poles" you mean the flattening parameter, measurements to date indicate that Mercury's polar and equatorial radii are nearly equal, for a flattening of approximately zero. New values derived from
MESSENGER data are being computed, and should be published in within a few months.

--David Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Will the messenger return to earth? If so, when will it be? I would like to know.Thanks, Matthew - submitted by Matthew S, Middle school student, 10-17-2012

MESSENGER was designed to orbit Mercury. It is not possible for it to return to Earth, nor would there be any reason to do so. You can browse a variety of questions related to the spacecraft's orbit and what might happen at the end of the mission here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I would like to reproduce your simulation of the MESSENGER orbit trajectory around Mercury after the MOI with STK HPOP. What values for the following parameters should I use? 1 - spacecraft mass; 2 - area/mass ratio for the spherical force model of the solar radiation solar; 3 - shadow model type (cylindrical or dual cone); 4 - third body gravity (planets considered); 5 - eclipsing bodies; 6 - More options of the force model. Thank you so much for your attention. - submitted by Julian Perez, College student, 05-11-2012

Here is the information you requested. You won't be able to exactly replicate the trajectory, since we use a specialized SRP model and Mercury gravity model. But you should be able to develop something very similar.
1.      The spacecraft mass after MOI was 575.419 kg, after the latest maneuver (OCM-8) the s/c mass was 515.886 kg
2.      For operations, we use an SRP model written in C# that breaks the craft into panels oriented based on the spacecraft's predicted attitude. For future trajectory estimates (when we don't have a predicted attitude C-kernel) we use a Heliocentric Spherical SRP model from STK's Astrogator propagator and an SRP area of 7.34891 m^2. As the mass changes throughout the orbit-phase, the area/mass ratio also changes. You would be able to implement this simpler model.
3.      When using the spherical SRP model, we use the dual cone shadow model and Apparent sun position. We also use a 1367.2 mean flux.
4.      Third bodies are modeled as point masses and include all other 7 planets, the Moon, and Pluto. We use the gravitational parameters associated with DE423 and the ephemeris for the third bodies from DE423.
5.      The only eclipsing body used is Mercury.
6.      We use the current IAU mercury physical parameters for Mercury. We also use a 20x20 mercury gravity model developed by our navigation team that is based on measurements from Mercury orbit, but has not been documented other than in a presentation at a MESSENGER science team meeting. The gravitational parameter of Mercury for this model is 2.203186091209334e+13 m^3/s^2. The General Relativity function from the STK Astrogator propagator is also used.
--Dawn Moessner, Johns Hopkins University Applied Physics Laboratory
MESSENGER Mission Design Team

I was wondering about the extended mission orbit. If the period drops from 12hr/ to 8hr, the highest point could change from 9,000 mi to 7,000 mi. I wanted to hear about the orbit, affects on heating cooling spacecraft, how much closer to thermal limits you can manage, etc, sensors new resolution, capacity. Thanks for the adventure.


- submitted by Robert Murphree, Interested public, 02-13-2012

Upon executing the set of maneuvers on April 16th and 20th, the orbital period of spacecraft around Mercury will be decreased from nearly 12 hours to exactly 8 hours. This set of maneuvers will have little effect on the periapse altitude, or closest point of approach in the orbit which will be near 280km at the time of these maneuvers but will significantly lower the apoapse altitude, the farthest point of approach from nearly 14,700km to 10,300 km. One of the primary benefits of reducing the orbital period will be the increase in the number of orbits the spacecraft will make around the planet from 2 orbit per day to 3 orbits per day. This 50% increase in orbital revolutions will effectively increase the amount of integrated time the spacecraft will spend closer to the planet. Some the benefits to this additional time close to the surface will be to increase the effectiveness for the various high energy spectrometers used to determine the composition of the planet's surface features in the Northern latitudes. This will also increase the number of altitude profiles ("tracks") the laser altimeter will be able to make in the Northern hemisphere, increasing the surface density allowing for more detailed topographic maps of this region of the planet. The decrease in the apoapse altitude will also allow for higher resolution images of the Southern Hemisphere of the planet in both monochrome and multispectral (color) bands.
There are two primary influences on the spacecraft and instrument temperatures in orbit around Mercury, seasonal effects and orbital period effects. The seasonal effects are generated due to a combination of the relative position of Mercury to the Sun, and the orientation of the spacecraft orbit to Mercury. This combined orbital geometry primarily contributes to the environmental heating of the spacecraft while in orbit. Seasonal heating effects increase slowly over the course of the mission as MESSENGER's orbital plane moves relative to Mercury under the influence of solar gravity. Increased heating during certain MESSENGER seasons of a few degrees Celsius for spacecraft components and instruments are expected over the next Earth year of Extended Mission operations due to these seasonal effect which are independent of the orbital period. The period effect which is directly related to the amount of time the spacecraft takes to orbit the planet primarily contributes to the cooling of the spacecraft following close exposure to the hot surface of the planet. After review of in-orbit data, almost all components on the spacecraft reached steady state cool temperatures within a few hours after peak heating rates near the closest approach point to the planet. During development of the MESSENGER mission, these cooling rates were expected, however to ensure mission success in an uncertain and previously unknown environment around the closest planet to the Sun, additional "cooling" margin was added in the form of orbital period time, ultimately settling on a 12 hour period due to other considerations for operational efficiency. After two complete Mercury years in orbit, 176 Earth days, the engineering team collected sufficient data to verify all thermal models, thus allowing some of the cooling time to be used to increase the amount and quality of scientific measurements collected during the Extended Mission. Note, one Mercury year is 88 Earth days, which is the time it takes Mercury to revolve around the Sun once.  Even with a 4-hour reduction in the "cooling" time, almost all instruments and spacecraft components reach steady state minimum temperatures with "cooling-time" remaining. Only a few components are expected to experience peak temperature increases on the order of approximately 5 degrees C when compared to current operational trends due to the reduction in orbital period. ALL components and instruments are expected to be operating well within established operational temperature limits during the extended mission.

--Eric Finnegan, Johns Hopkins University Applied Physics Laboratory
MESSENGER Mission Systems Engineer

Hello, Excuse my ignorance but you can use the remaining fuel of MESSENGER to make a soft landing on the planet in order to use the tools on board to make the transmission of any data or other information can be transmitted or to take pictures of the surface planet before the probe is destroyed. It would be an interesting alternative instead of extended the life of the satellite for one year. A soft landing of the probe instead to impact to the ground would be more interesting. Forever if it is technically possible. Greetings. Carlo - submitted by Carlo Facchini, 02-02-2012

Read this answer to a similar question from another fan of space exploration. The amount of energy needed to land on Mercury far exceeds the capacity of MESSENGER's propulsion system, even with the amount of fuel carried at launch. A spacecraft designed to land would need to carry much more fuel, and hence would need to be launched from Earth using a larger rocket. This would greatly increase the cost of the mission. Hopefully some day humans will undertake such a mission. "Ground truth" measurements of the composition of the rocks would be tremendously valuable for furthering our understanding of Mercury and its relation to the other planets.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why an elliptical orbit instead of an circular orbit around Mercury? Is it because the perigee(shorter radius of the ellipse?) is 120 mi and if the apogee(9000 mi) is further reduced, the resulting smaller perigee might end up crashing the spacecraft? Thanks! Venkata Pappu. - entered by Q&A admin, 01-25-2012

You can find an answer to a similar question on the MESSENGER Q&A website. There you can browse previous questions and answers. Listings by category are given here. And if you have questions in the future, you can use the "Ask Question" button on this page to enter your question through the system. Thanks for your interest in planetary exploration and MESSENGER.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Additional information from Jim McAdams, Johns Hopkins University Applied Physics Laboratory, MESSENGER Mission Design Lead Engineer: The reason that an elliptical orbit around Mercury was chosen over a circular orbit is that the launch vehicle lift capability and spacecraft propulsion tank size were together insufficient to deliver a spacecraft to a circular or even much less elliptical orbit at Mercury. The MESSENGER spacecraft launched on August 3, 2004 on a Delta II-7925H (H for "heavy-lift") expendable launch vehicle, the largest rocket allowed by NASA as of 1999. The spacecraft dry mass and propellant load was limited to be at the upper limit allowed for the most demanding day in the late-July to mid-August 2004 launch period. To be able to load on the spacecraft the extra propellant needed to enter circular orbit about Mercury would have required a larger launch vehicle carrying a larger spacecraft with larger propellant tanks.

Hi, This is Carsten Menkhoff from Germany. I've a question about this global picture of Mercury: Mercury Globe: North Pole Release Date: December 2, 2011. Will the remaining coverage gap be closed during the MESSENGER mission? - entered by Q&A admin, 01-17-2012

The northern most portion of Mercury is challenging to image due to MESSENGER's highly elliptical orbit. The spacecraft passes only about 200 km above Mercury's surface at its minimum altitude in the north, and at that altitude, even the footprint of MDIS's Wide Angle Camera (WAC) is small; thus, many images are needed to cover an entire region. Also, the orbit does not pass over the north pole. MDIS has a pivot, which can be used to look to the side, but to acquire images north of a latitude of about 85° also requires the spacecraft to point to the side, which is disruptive to the operations of MESSENGER's other instruments. During the recently funded extended mission, one of the MDIS imaging campaigns will be dedicated to imaging Mercury's northern most region, and those images will finally fill in this small gap of still unseen terrain!

--Nancy Chabot, Johns Hopkins University Applied Physics Laboratory
MESSENGER MDIS Instrument Scientist

Just wanted to offer a heartfelt congratulations to the MESSENGER staff on winning the mission extension! This is a first class mission of exploration being conducted by an awesome group of dedicated people. I am only an interested observer, but everyone on the MESSENGER staff has made feel I was truly a part of it. Thank you and good luck with the continued exploration! 

- submitted by Bryce Johnson, Journalist, 11-27-2011

Bryce - Thank you. The team is very happy that MESSENGER can continue to explore Mercury for another Earth year. And it is wonderful to know that members of the worldwide public take an interest in the mission.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

How long will MESSENGER continue to send data? - submitted by Jack S., Middle school student, 10-10-2011

MESSENGER's primary mission will end in March of 2012. The project has submitted a proposal to NASA for an extended mission. If the extended mission is funded, the spacecraft will be operated for one more Earth year.

You can browse previous questions related to the orbit and possible end-of-mission scenarios here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Three questions relating the eventual fate of MESSENGER: (A) I have read that data collection will end in March 2012 and that several years after the mission officially ends MESSENGER will impact on Mercury. Now that MESSENGER has been in orbit of Mercury for six months (October 2011) is it known roughly when MESSENGER is expected to impact on the planet's surface?
(B) Will it be possible to calculate the rough location of the expected area of impact before MESSENGER actually impacts?
(C) If missions arrive in orbit of Mercury in the future and it becomes possible to compare MESSENGER's impact site with images taken of that area by MESSENGER while in orbit, in what ways could the impact site further understanding of the surface of Mercury? - submitted by Tim, Interested public, 10-10-2011

[A] and [B]. The MESSENGER project has submitted a proposal to NASA for funding of an extended mission for one additional Earth year after completion of the primary mission. Some modifications to the orbit would likely be made for the extended mission. So it is too soon to tell where the spacecraft might strike the surface. Even if it we know the state of the orbit at the time that the final trajectory correction maneuver is conducted, it might be hard to predict the exact impact time and location, because of perturbations to the motion by Mercury's non-uniform gravity, by variations in radiation pressure on the spacecraft depending on its orientation to the Sun (if attitude control is lost), and by solar gravity.

[C]. The European Space Agency's BepiColombo orbiter is scheduled to arrive at Mercury a few years after MESSENGER's mission is complete. The crater made by MESSENGER's impact might be only a few meters in diameter. The best resolution of MESSENGER images is about 10 meters per pixel (and that is just for special targeted images that cover only a very small fraction of the planet's surface). Therefore comparison with BepiColombo images (even if they have high enough resolution to see the MESSENGER crater) would be very challenging.

You may like to browse other related questions in the Q&A "Orbiting Mercury" topic.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

After the mission is over what will happen to the spacecraft? Will it crash into mercury or just stay in orbit? - submitted by fred, Interested public, 10-02-2011

This topic is covered by several previous questions in the Orbiting Mercury section of the Q&A. Browse through to learn more about MESSENGER's ultimate fate.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

How long does it take for MESSENGER to orbit Mercury? - submitted by Ethan crow, Elementary school student, 09-29-2011

The spacecraft is in a 12-hour orbit. Read more about the orbit here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Reasearching on messenger I came accross the fact that it has an elliptical orbit around mercury, and after reading through i got to know the reasons for it. But is it even possible for any sattellite to be in a circular orbit around mercury if the altitude may not be low enough to heat up the settlement? - submitted by Waqih Ashfaq, High school student, 08-23-2011

There are several challenges for spacecraft in low orbits around Mercury. One is gravitational perturbation from the Sun. MESSENGER must occasionally use its propulsion system to perform orbital correction maneuvers. These rocket "burns" reset the orbit to its desired dimensions and period. A second hazard is the blast of reflected sunlight and emitted infrared radiation coming up from the hot surface of the planet. This problem is most acute when the spacecraft is in a "noon-midnight" orbit, that is, flying directly between the Sun and the planet on the dayside. During these times, special measures are taken to manage the thermal loads on the spacecraft.

For these reasons it would be quite difficult to maintain a close, circular orbit around Mercury. MESSENGER is in a highly elliptical orbit, bringing it as close as 200 km to the surface and about 15,000 km at the farthest point. BepiColombo, a joint European-Japanese mission that will be launched in 2014, will send two spacecraft to Mercury. One, the planetary orbiter, will be in an elliptical orbit 400 x 1500 km. The magnetospheric orbiter will follow an orbit more similar to MESSENGER's: 400 x 12,000 km.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Did you guys need to adjust the speed of the probe in orbit than initially calculated? Or did calculations go to plan? Did you have to slow the craft than originally calculated? What calculations did you use? - submitted by jason, Interested public, 06-16-2011

The physics of spacecraft trajectories are quite well understood, allowing the MESSENGER Mission Design Team to make highly accurate calculations of the spacecraft's motion. For example, the Table in the answer to another question lists the target and actual orbital parameters for MESSENGER's orbit insertion.

As another example, on 15 June 2011, the first orbit-correction maneuver (OCM-1) was completed successfully. The new periapsis altitude was within a few hundred meters of the target value of 200 km, and the orbital period was within seconds of the 11.83-hr target. Read more about mission design in this Q&A.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What are the foci distance and the length of the major axis of the orbit of MESSENGER? I would like to have my students find the eccentricity of MESSENGER's orbital ellipse. Thanks! - submitted by Jane Gilbride MESSENGER fellow, K-12 teacher, 05-25-2011

MESSENGER's orbit is slowly evolving due to perturbations mainly from the Sun and Mercury's gravity field. On 2011 MAY 25 10:38:32 UTC (the periapsis of orbit #136), the spacecraft's orbital elements relative to Mercury were: semi-major axis = 10174.86 km, eccentricity = 0.721115, inclination = 83.2 deg, longitude of ascending node = 349.0 deg, argument of periapsis = 117.3 deg, radius of periapsis = 2837.62 km, and period = 43460 sec. So, the length of the major axis at this time would be 20349.72 km and the distance between the foci would be 14674.48 km.

--Dawn Moessner, Johns Hopkins University Applied Physics Laboratory
MESSENGER Mission Design Team

Hello. Your web site does not give any information on parameters of the orbit. Are any figures available and do you intend to publish them?   Regards, Bob Christy - entered by Q&A admin, 04-22-2011

General information and graphics concerning the spacecraft's orbit about Mercury can be found here and here. You can see some actual values for the orbital parameters in the answers to two previous questions.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

 A. After the probe completes its final orbit in March 2012, what's in store for it? The site is silent on this point. B. And a silly question: Do you guys ever personalize your probes? If it was me, I'd sign my name on a panel somewhere in Magic Marker.  I'll be thinking about MESSENGER's fifth OCM on 05-Dec, which happens to be my 57th birthday.  regards, Paul Havemann - entered by Q&A admin, 04-21-2011

A. The end of the mission is discussed in several of the questions under the "Orbiting Mercury" category:

B. You'd have to check with the actual engineers and technicians who constructed the spacecraft. However, I doubt that magic markers are space qualified. The volatile compounds in the ink could evaporate once in space, leading to contamination of camera optics or otherwise causing a problem.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why doesn't MESSENGER strive for a circular or slightly elliptical orbit versus a highly elliptical orbit it now occupies (something to do with that massive core?). [ Since MESSENGER is "near polar," are you compensating for any type of argument of perigee drift? ... Is that a bad thing? ]

Other than aesthetics, you'd think the photographic scale would be easier to match, without the use of "fractal filler noise" in photographs at apogee. If the planet were a fast spinner, I could see the utility of a quick pass at perigee, for Doppler comparison.   from Dave Lazok - entered by Q&A admin, 04-01-2011

The elliptical orbit was chosen mainly for purposes of thermal management, as you can read on this page. Learn more about the orbit and maintenance maneuvers here.

MESSENGER's cameras are working to produce a monochrome basemap at 250 meters/pixel spatial resolution and a global multispectral (color) image dataset at 2 kilometers/pixel. Images are sometimes binned (reduced in resolution) on the spacecraft to help match the resolution in different parts of these mosaics. Binning also decreases the volume of data that must be downlinked to Earth.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

It looks like MESSENGER is initially in a polar dawn-to-dusk orbit - more or less staying over the terminator.Will the orbital plane stay fixed - so the orbit will cycle from dawn-to-dusk to day-to-night and back - or will it precess to keep MESSENGER over the terminator througout the mission? - submitted by Kurt Hillig, Interested public, 03-31-2011

The orbital plane is fixed and the planet rotates beneath, so that the spacecraft will experience both noon-midnight and dawn-dusk orbits. Read more about the orbit here and here.

What is the closest MESSENGERwill get to the planet's surface during the orbital phase of the mission ? - submitted by Sam Jones, Interested public, 03-31-2011

The closest point in the orbit is right about 200 kilometers (120 miles).

So many stats on orbits, didn't see 'Time for each (1) orbit' displayed. - submitted by Stu, Interested public, 03-31-2011

MESSENGER's orbit has a period of 12 hours.

Will MESSENGER continue on to another planet, or is this the end of the line, once the Mercury mission is complete and how long will MESSENGER stay around Mercury sending images. - submitted by Tim Smith, College student, 03-30-2011

The entire team is looking forward to a successful primary mission (one Earth year in length), and is hoping that
NASA will approve an extended mission for another Earth year. There should be enough fuel remaining at the end of the primary mission to maintain the orbit against perturbations from the Sun's gravity for another year of operations. However, at some point MESSENGER will run out of propellant and will be unable to maintain its orbit; it will eventually crash into the surface of Mercury. Perhaps the European Space Agency's BepiColombo orbiter, scheduled to arrive at Mercury a few years after MESSENGER's mission is complete, will be able to find a tiny new crater - formed from MESSENGER's impact.

--David Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Considering the eleaborate orbits that the probe around Jupiter has made are you sure that the MESSENGER crew is experienced enough in orbital mechanics to maximize the fuel available to get maximum orbit time? Why wasnt a more circular orbit considered rather than the eliptical one the spacecraft is flying at this time. Perhaps a burn at an appropriate point in the orbit could give the probe a more cicular orbit and prevent this demise. Sems the sun will keep the solar cells energy level up and the passive shielding will keep the spacecraft electronics safe. Why this disposal mentality?


- submitted by Edward J Cox, Interested public, 03-30-2011

MESSENGER's orbit was selected for reasons of dynamics and thermal control. A circular orbit would be energetically much more difficult to maintain, and hence require the spacecraft to carry a larger fuel load (which would mean larger fuel tanks, a larger rocket to lauch the spacecraft and hence costs far beyond the cost cap of NASA's Discovery program). The highly elliptical orbit also limits the time that the spacecraft spends at low altitudes above Mercury's scorching surface; the infrared radiation coming up from the planet can be several times greater than the intensity of the Sun at Earth's distance. So essentially MESSENGER swoops in for a mapping pass, then arcs back out far from the planet to cool down and transmit data to Earth before diving back again. Lots more information on the orbit can be found on the website here and here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I read on your website that once the MESSENGER mission is over, the spacecraft will simply be crashed into Mercury's surface. This seems like the galactic version of littering to me. As such, why not simply direct the spacecraft straight up (relative to the plane of the solar system) or send it into the Sun? By sending the spacecraft up (or into the Sun) and not crashing it into Mercury, the expended craft will be disposed of without having an impact on Mercury or its beautiful, pristine, and untouched surface. - submitted by Alan, Interested public, 03-30-2011

It is correct that MESSENGER will eventually run out of fuel, be unable to maintain its orbit, and crash into the surface of the planet. The type of maneuvers that you suggest (moving up out of the ecliptic plane, or leaving Mercury orbit for one that intersects the Sun) would take a TREMENDOUS amount of energy - far beyond the capability of MESSENGER's propulsion system.

Mercury's surface is certainly beautiful. But I'm not sure that "pristine" and "untouched" are good descriptors. For 4.5 billion years, natural objects of all sizes (asteroids, comets, interplanetary dust) have been striking the planet, producing the cratered landscape we see today. Billions of these impactors have masses greater than that of the spacecraft, and they hit with velocities many times faster than MESSENGER's. One tiny new crater is a small price for bringing humankind a bounty of information about one of the Earth's closest siblings, helping us to better understand our home planet and its place in the Solar System.

Incidentally, for planetary bodies that could conceivably support life (like Mars or Jupiter's moon Europa), NASA's "Planetary Protection" rules require a certain level of sterilization for spacecraft that have the potential to impact the surface. The goal of these rules is to prevent biological contamination by microbes from the Earth.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

As the MESSENGER team effectively used the spacecraft as a solar sail to alter its trajectory in the proximity of the Sun, is the Sun's solar wind (plasma) sufficiently dense at the orbit of Mercury to cause some drag on the planet similar to the drag effect Earth's rarified atmosphere has on spacecraft in low Earth orbit? If so, how would this drag affect Mercury's orbit over time? - submitted by Ralph Ricketson, Interested public, 03-25-2011

The solar wind density near Mercury is ~500 per cubic centimeter, comparable to those in the Earth's exosphere near geosynchronous orbit (about 35,000 km altitude); drag on geosynchronous satellites is totally negligible.

The low-Earth orbits where drag effects are important are in the thermosphere. This is the realm of orbiters like the Space Shuttle or International Space
Station (the ISS's orbit is at an altitude of 278 to 460 km). Because of this drag, the orbit of the ISS must periodically be raised.

Photon (radiation) pressure by far dominates the non-gravitational forces on MESSENGER. This is taken into account in all of the trajectory calculations, and used to advantage in solar sailing.

--Tom Krimigis, MESSENGER Atmosphere and Magnetosphere Group & Ralph McNutt, MESSENGER Project Scientist

Johns Hopkins University Applied Physics Laboratory

What were the actual numbers vs. predicted after orbit insertion for the following: orbital period, inclination, periapsis, apoapsis? - submitted by Michael Clyde, Interested public, 03-19-2011

Parameter Actual Target Orbit period (s) 43456.9 43195.5 Periapse altitude (km) 206.79 200 Semimajor axis (km) 10176 10135 Eccentricity 0.740 0.740 Inclination (deg) 82.52 82.5 RA of Ascend Node (deg) 350.16 350.17 Arg of Periapsis (deg) 119.16 119.13 Periapsis Latitude (deg) 59.997 60 Periaps crossing time 12:52:19.8 12:47:56.0

Please can you tell me details of MESSENGER's primary orbit and future orbits. - submitted by william ripley, Interested public, 03-18-2011

In a note to the team very early (eastern time) on March 18, 2011, Mission Spacecraft and Systems Engineer Eric Finnegan reported the following:

"Using initial acceleration data from the spacecraft following the burn, the Navigation team has estimated the initial preliminary post-burn orbit of MESSENGER about Mercury as:
Periherm Altitude = 203.21 km
Semimajor Axis = 10151.31 km
Eccentricity = 0.740
Inclination = 82.51 deg
Right Ascension of the Ascending Node = 350.17 deg
Argument of Periapse = 119.17 deg
Orbital Period = 12h 1m 38.8s
This initial estimate will be refined over the next 24 hours as the navigation team gathers radiometric data and releases the first in-orbit orbit determination of the mission."

What will happen to the craft after it completes its mission? - submitted by snickers, K-12 teacher, 03-18-2011

The entire team is looking forward to a successful primary mission (one Earth year in length), and is hoping that
NASA will approve an extended mission for another Earth year. There should be enough fuel remaining at the end of the primary mission to maintain the orbit against perturbations from the Sun's gravity for another year of operations. However, at some point MESSENGER will run out of propellant and will be unable to maintain its orbit; it will eventually crash into the surface of Mercury. Perhaps the European Space Agency's BepiColombo orbiter, scheduled to arrive at Mercury a few years after MESSENGER's mission is complete, will be able to find a tiny new crater - formed from MESSENGER's impact.

--David Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Could there be enough fuel left after capture and orbit keeping to shift the MESSENGER periapsis to be over the south pole of Mercury if something especially interesting was found there?

- submitted by Mark Gaponoff, Interested public, 03-17-2011

The entire team is looking forward to a successful primary mission (one Earth year in length), and is hoping that
NASA will approve an extended mission. For the extended mission, it would not be possible to change the
orbit so that the closest approach (periapsis, or periherm) is over the southern hemisphere - that would
require far more fuel than the spacecraft has available. However, some far less radical modifications to the orbit are being considered.

All about impact craters, the dominant landform on Mercury

Dear Sir, I was thrilled and gratified to learn recently that a crater was named 'Tyagaraja', a great musician of the 17-18th centuries from South India. Here is a link from your website related to this. I would appreciate if you could share any information about how his name came to be chosen. For example, what was the process, who were the people involved in the selection etc. Many Thanks in advance. Regards, Prabhakar

  - submitted by Prabhakar Chitrapu, Interested public, 01-07-2015

Tyagaraja is one of the most fascinating features on Mercury. The crater name was assigned by the International Astronomical Union (IAU) in 1976, based on images of Mercury's surface returned by NASA's Mariner 10 spacecraft. According the the IAU theme, impact craters on Mercury are named for "Deceased artists, musicians, painters, and authors who have made outstanding or fundamental contributions to their field and have been recognized as art historically significant figures for more than 50 years."  The specific person who suggested this name may be lost to history, but the IAU strives to include worthy individuals from all over the world. So the name Tyagaraja was included based on his accomplishments.
If you would like to offer a suggestion for naming a crater on Mercury, you could enter the contest that is underway until January 15, 2015.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

what role did impactors such as meteorites and comets play in making our beautiful mountain scene? - submitted by Brianna, High school student, 05-28-2014

I'm not certain to which particular "beautiful mountain scene" your refer. But impact cratering is perhaps the most fundamental geological processes that has taken place on the solid-surface bodies in our Solar System. Meteoroids, asteroids, and comets collide with Mercury with incredible violence, excavating holes in the target surface and melting and vaporizing considerable quantities of the target and impactor material. Impact craters have raised rims, and for the largest craters, called "basins", these rims appear as long circular mountain ranges. For example, the "Caloris Montes" form the rim of the Caloris impact basin. On Mercury, craters larger than about 12 km (7 miles) in diameter have central peak mountains. For craters larger than about 125 km the central peaks can take the form of a mountain cluster or ring, for example Eminescu. On Earth, the mountain ranges that we see today are mostly a result of volcanic and tectonic activity.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

The Oct. 21 2013 Gallery image shows what appears to be a channel from a subsidence flowing into and cutting through the crater wall.   Nigel Lavery - entered by Q&A admin, 10-25-2013

You have identified what may be a fault scarp that begins in about the middle of the bright orange-floored crater and extends at about the 7 o'clock position, continues across the floor of Matisse and up Matisse's wall and onto the exterior. The geology is complicated by the presence of many chains of secondary craters that were formed by the impact that created the orange-floored crater.

There are a number of locations on Mercury where fracturing associated with a scarp appears to have provided a pathway for melts generated at depth to gain access to the surface and feed volcanic eruptions. This might explain the association of the scarp with the vent and pyroclastic deposit (bright orange material). Another example is found in the extreme lower left corner of the image, where a prominnent lobate scarp cuts across a flooded crater that has an irregular depression (vent) on its floor.

--Dave Blewett, Johns Hopkins University Applied Physics Lab
MESSENGER Participating Scientist

Surely that is a volcanic vent at the centre just off the edge of the secondary secondary impact?  Picture ref EN025157794 - submitted by Nigel Lavery, Interested public, 10-01-2013

You are referring to the Sept. 30, 2013 gallery image of Neruda crater. Neruda's central peak was partially destroyed by an impact, as seen by the mostly circular, raised rim crater on the eastern side of the peak cluster. As you have noticed, immediately to the west of this impact is what appears to be an irregular depression that may cut the central peak. It is possible that the irregular depression is a volcanic vent, similar to those seen in association with central peaks of other Mercury craters (like Tyagaraja). However, the shadows cast by the peaks in this image make it difficult to determine conclusively. Another piece of evidence that may point to the irregular depression being a volcanic vent is that the area around the peak appears to have a slightly higher reflectance, consistent with the presence of high-albedo pyroclastic material (see this color image; Neruda is near the center of the image).

--Rachel Klima and Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Geology Discipline Group

What is the vertical exaggeration on the August 2, 2013 3-d crater image? Also does the crater have a name? - submitted by Mary Ann Hager, 08-02-2013

The crater featured in the August 2, 2013 anaglyph does not yet have a name. The amount of vertical exaggeration in of 3-D images of this type is rather difficult to specify. But to give you a sense of the true elevation difference, a measurement of the crater's topography indicates that the height of the crater wall is about 2100 m (6890 ft.) above the floor.

--Ariel Deutsch, MESSENGER MDIS summer intern
Nancy Chabot, MDIS instrument scientist

is the evidence for molten lava in the Hokusai basin? Explain please. - submitted by joe molinar, College student, 04-14-2013

Hokusai, 95 km in diameter, is one of the most impressive rayed impact craters on Mercury. When comets or asteroids strike Mercury, they are traveling faster than the speed of sound in the target rocks. Hence such collisions are termed "hypervelocity" impacts. In these events, tremendous quantities of the target material are vaporized, excavated and ejected, and melted. Some of the molten rock may pool in the floor of the crater or collect in low spots on the wall terraces or ejecta blanket. In this spectacular image, you can see the smooth surface formed by the solidified melt on Hokusai's floor. Also visible are small ponds on the wall terraces and possible channels were melt drained down the walls to the floor. Being molten rock, impact melt deposits share some characteristics with volcanic deposits formed by erupted lava melted by internal heating within Mercury's mantle. Many smooth plains deposits on Mercury were formed by massive outpourings of lava.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

 i work as a Library Tech Asst at a school. WHO did the nominations for the names for newly found craters on Mercury? Specifically: WHO nominated "Lovecraft" (if this process is not confidential)? my NON-work time i am associated w/a group in Providence RI that is sponsoring a Convention dedicated to HP Lovecraft and want to make this person aware of the fact--if not more (inre having them guest, if funds avail themselves) =) Thanks for Your time in reading/reponding to this.  JShea - submitted by Joe Shea, College instructor, 04-03-2013

The name "Lovecraft" was proposed for a Mercury crater at 86 degrees S, 286 degrees E by a member of the MESSENGER science team. The name was approved by the IAU in March, 2013.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Hi, we are making a planetarium show about possible landing sites and we'd love to feature Tolkien crater. Do you have a full-planet DEM of Mercury, with possible higher resolution of Tolkien?Thanks very much... - submitted by Patricia Reiff, College instructor, 01-23-2013

Tolkien crater is about 50 km in diameter. Data from the Mercury Laser Altimeter (MLA) indicate that the crater is about 2 km deep, with a central peak that is at least 1.7 km high. MLA altimeter profiles from the Primary Mission were released to the public through the NASA
Planetary Data System (PDS) on September 7, 2012. MLA altimeter profiles through September 17, 2012 and an MLA-derived northern hemisphere digital elevation map using these data will be released on March 8, 2013.

--Carolyn Ernst, Johns Hopkins University Applied Physics Laboratory
MLA Deputy Instrument Scientist

Im teaching a 7th graders about the new information brought back by the Messenger on the planet Mercury and the one topic Im trying to focus on is how the craters on the surface of Mercury differ from those of the moon. From the articles Im reading online, the craters on the moon have rims which indicate impact of meteorites however the ones on the surface of Mercury differ in that they are rimless and there are smooth surfaces indicating volcanic activity. 1. How can I explain what caused the surface of mercury to look more like popped blisters for lack of a better word. 2. How did the volcanic activity occur on the surface of the planet...did the iron core heat up and cause lava to come to the surface. 3. If the planet mercury is lacking an atmosphere what is protecting it from the suns solar activity, why hasnt it burned up and how does the magnetic field play a part in protecting the planet from the sun.4 does the long exposure of the surface of the mercury to the sun, due to the slow rotation (59 days) and then the quick cooling off have anything to do with how the surface of the planet looks...(ie..the blistering look it has and the scarps due to the long period of exposure to heat and then extreme cool temperatures.Any suggestions on what experiments I can do in class regarding the new discoveries about the planet mercury?Thank you - submitted by sheila, Other educator, 10-01-2012

 The surfaces of both the Moon and Mercury are dominated by impact craters. Newly formed impact craters have raised rims and floors that are below the level of the surrounding terrain.
Some craters, particularly large ones (more than about 200 km in diameter, called "basins"), on both bodies were later filled in with volcanic material in the form of smooth plains. On the Moon, the smooth plains ("maria", Latin for "seas") are darker than the rugged highland surfaces. On Mercury, the smooth plains generally do not show the strong brightness contrast with the more rugged highland-like terrain. The smooth plains were formed by lava flows, what we call "effusive" volcanism.
On both the Moon and Mercury, there are also a few examples of volcanic craters, that is, vents that were the source of explosive volcanic eruptions. These eruptions deposited pyroclastic material (sometimes called "volcanic ash") around the source vents. On the Moon, these pyroclastic deposits are dark, whereas on Mercury the pyroclastic materials are brighter than the surroundings. These differences in the brightness of the materials reflect compositional differences between Mercury and the Moon. Volcanic vents are rimless and generally are not circular (most impact craters are circular).
Volcanic activity occurs when the internal heat within a body is enough to cause the rocks in the interior to partially melt, and the melts are able to rise to the surface and erupt. Depending on the gas content of the melts, the eruptions may be either effusive (lavas - lower gas), or explosive (pyroclastic - high gas content). The heating may be due to the heat of formation (as the body accreted from dust in the early days of the Solar System), from heat generated by decay of naturally occurring radioactive elements (like aluminum-26, iron-60, potassium-40, uranium, or thorium), or by tidal heating. Accretional and radiogenic heating probably dominated on the Moon and Mercury; tidal heating produces the high degree of volcanic activity on Jupiter's moon Io. The internal heat of the Earth today is produced by radiogenic heating.
Daytime surface temperatures on Mercury can reach about 800 degrees F. The melting temperatures of the surface rocks however are about 2000 degrees F or higher. Thus the Sun's heat is not enough to greatly modify the surface. (Of course, rocks (except for coal) do not burn, and "burning" in the normal sense requires oxygen.)

Mercury has a weak internal magnetic field - similar to Earth's, but not as strong. The magnetic field can partially protect Mercury's surface from the solar wind. The solar wind is the stream of charged particles, mainly protons and electrons, that stream out from the Sun. These solar wind particles hit the surfaces of airless bodies (like Mercury, the Moon, and asteroids) and can cause darkening and color changes of the uppermost surfaces. Mercury's magnetic field partly protects the surface from the solar wind, but at times (during "magnetic storms"), the solar wind can get in and hit the surface.

The abundant scarps (cliffs) seen on Mercury were caused by compressive (squeezing together) forces within Mercury's crust. These forces resulted from contraction of the planet's interior as it cooled. The cliffs are the surface expression of what geologists call "thrust faults", or places where the compressive forces caused the crust to fracture and one section of crust was pushed over another section as the sections slid along the fault.
The MESSENGER project's Education and Public Outreach website has extensive resources for teachers and students, including classroom activities.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist


I have two questions to ask about craters:
First, because mercury have an atmosphere (and this could be applied to all planets with one) could be the reason (conclusions taken roughly by me because i'm not an expert in astronomy) are the explanation to all (or the majority) the craters are rounded? (Objects with oblique trajectories have less probabilities to reach the surface because they travel more time in the atmosphere). If this thought is right, why we see the same type of craters in the moon?
Second question: By what it was explain to me, the hollows were created by the compression and decompression of Mercury crust. I thought this was the reason too because the orbit of mercury is so eccentric creating extreme conditions in the surface. But what about volatilization of materials caused by solar wind? Could less resistant materials to volatilization be the reason to the formation of this hollows? This explain (i think) is less reasonable because it implies that this materials are rare. But could be a reason or is it immediately excluded? - submitted by Sergio Silva, Interested public, 08-31-2012

The question of why impact craters are circular often arises - see here and here.
Scarps are formed by compressive forces within the crust. See this for the effects of solar heating on surface materials.

With regard to the formation of the hollows, read this Q&A. The formation of hollows is not directly related to tectonic forces, but is probably a result of loss of some volatile

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

The gallery image for April 23rd features a scarp illuminated from the west (north being towards the right of the picture) and shows an intriguing feature that was not mentioned in the description. On the left of the scarp there is a crater with a complex structure - mostly in the dark - that appears very similar to many volcanic vent features found on Mercury so far. Could this be real? Or is it just a result of the lighting angle? It is interesting to think of a volcanic vent right on a scarp/fault line. . . .  - submitted by Bryce Johnson, Journalist, 04-23-2012

You have indeed found an example of a pit-floor crater, one that has been modified by the lobate scarp that cuts the crater and the pit. Pits such as these probably formed through volcanic activity, either related to an explosive eruption or by collapse following withdrawal of magma from beneath the crater floor.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

In image 1320489, showing the floor of Abedin crater, is the terrain in the upper left part of the rim or of the central peak?

- submitted by Vanessa, 03-23-2012

The image shows the northwest portion of Abedin crater, so that the terrain in the upper left is part of the crater rim's inner wall. The wall is characterized by dozens of small terraces, interpreted to have formed due to collapse of the crater wall immediately after impact. The smooth areas within the terraces probably correspond to impact melt deposits related to the impact.

--Paul Byrne, Carnegie Institution of Washington
MESSENGER Geology Discipline Group

Is there a way to determine the elevation difference of the crater floor and the central peaks in image 1353328? Thanks. - submitted by Mike Reynolds, Interested public, 02-17-2012

You are referring to an image of the crater Amaral. We have updated the image caption to include the incidence angle of the sunlight at the time the image was collected. From this and the pixel resolution of the image, you can use trigonometry to calculate the height of the peak from the length of the peak's shadow.

--Dave Blewett and Nancy Chabot, Johns Hopkins University Applied Physics Laboratory
MESSENGER Geology Discipline Group

Image ID: 911007
Center Latitude: -1.98°, Center Longitude: 354.1° E
Scale: The crater at center is approximately 90 km (56 miles) across

named Emry Crater? Is there a program in place I could apply to or is this an idea to get the public more involved with the MESSENGER mission?

Let me know, Chuck Emry, Very interested public - submitted by Chuck Emry, Interested public, 11-13-2011

See this previous Q&A regarding naming of features on Mercury. You can learn more about planetary nomenclature here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory, MESSENGER Participating Scientist



The Gallery image "Oblique impact" is surely a misnomer? Hypervelocity impacts, typical of  the size and shape of those shown, are always circular.  The image shows a triple impact, with three clearly circular craters, superimposed. Is it not more likely that this triple crater is a short crater chain, made when an in-bound body fragemented in Mercury's gravity field or else the Sun's, in the same way that Shoemaker-Levy did before hititng Jupiter? - submitted by John Davies, Interested public, 10-24-2011

Hypervelocity impacts usually produce circular craters except when the angle of approach is less than 15 degrees above the horizontal. We interpreted the elongated crater as
the result of such a low-angle oblique impact, which produced the elongated central ridge (corresponding to the central peak in a circular crater).

An older circular crater is cut by the southwestern end of the elongated feature, indicating that the circular crater formed first.

However, it is possible that the elongated feature was formed by near-simultaneous cratering by several impactors that each formed a circular crater. There are some scallops on the walls of the elongated crater that could be remnants of the outlines of individual circular craters. Or the the scallops could have been formed by later slumping (landsliding) that modified the wall of a single elongated crater.

--Carolyn Ernst and Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Geology Discipline Group

The featured image of Kuiper crater prompts me to ask about this. Why is it that two large craters sitting next to each other can be identical in every way, but only one will have a central 'rebound' mountain feature while the other has a totally flat floor? We see this a lot on Mercury. It is puzzling! - submitted by Bryce Johnson, Journalist, 10-08-2011

The image to which you are referring shows two large impact craters of about the same size. Kuiper formed on the northwestern rim of one of them (Murasaki). Murasaki has a central peak, while the similar-sized crater to its east (right) does not. The rim of the eastern crater is somewhat more degraded than Murasaki's, suggesting that it might be older. The eastern crater's peak may have been smaller to begin with because of differences in the target materials or the impact conditions (speed, size and approach angle of the impactor). Or the peak could have been destroyed by impacts or volcanism. There are hints of a ghost crater on the southeastern floor of the eastern crater. The formation of the ghost crater might have removed the central peak, and then volcanic activity filled in the ghost crater and other parts of the eastern crater's floor.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

The round craters on Mercury look exactly like high-intensity plasma craters. This idea has been around for decades, yet most scientists ignore this more plausible explanation for the creation of the craters. It is now well known that plasma permeates space and that plasma is highly conductive, and these images can be created by plasma discharges in laboratories that duplicate the look of these craters. Why then is this plausible explanation brushed aside in lieu of one that does not match observation? Impact craters would not, in my observation, be round and devoid of the supposed material that we are told to believe created the impact. These craters look like electrical machining, but not impact craters. Why are not told of more plausible explanations to the cratering? - submitted by Evonne K, 09-30-2011

For many years before the Apollo landings on the Moon there was vigorous debate about the origin of craters. However, formation by impact is now accepted as the explanation. What is the evidence? The three major avenues that have provided insight into this problem are laboratory experiments, fieldwork (on Earth and the Moon!), and remote observations of planetary surfaces like those from MESSENGER.

First, scientists have done numerous controlled experiments shooting impactors at target materials in the lab at interplanetary velocities ("hypervelocity impacts", see here and here), and these produce craters with characteristics like those seen on the planets. In fact, by varying the conditions of the impact experiments, such as the material being impacted and the impact angle, scientists have gained additional insight into the features we see on the planets. One of the results of these experiments is to make clear that impact craters end up being circular under most impact conditions (even at fairly oblique impact angles), and that because of the high energy of crater-forming event, the impactor itself is often vaporized and destroyed. Second, exploration of craters on Earth and the Moon have led to the discovery of minerals that experienced shock -- in other words, they have a variety of characteristics which in detail allow us to infer that the rocks experienced a short period of very high pressure. This is consistent with the passage of a shock wave during crater formation. Third, scientists doing remote observations have investigated impact
crater populations on various planetary bodies, such as Mercury and the Moon, and found major similarities between these crater populations. It turns out the size distribution of craters we observe
on the planets agrees very well with what we would expect to form from objects lurking in the inner Solar System that we know are potential impactors and whose sizes have been characterized with telescopic observations.

In summary, we have developed a good understanding of cratering based on impact experiments in the laboratory, and we can recognize these tell-tale characteristics in nature on Earth and the planets. This is what makes the theory of impact cratering robust -- it provides a consistent explanation for a variety of observations. In recent years, on the planet Mars, we have even seen new craters form between observations by spacecraft, and the rate at which these have formed seems to match reasonably well with what had been predicted. Besides being extremely cool, this sort of new observation is exciting, since it can help to further refine our understanding of the impact process, and to ask new questions that hadn't been anticipated.
This is precisely how science progresses.

-Caleb Fassett, Brown University
MESSENGER Geology Discipline Group

Based on the current theories of planetary formation with an accretion disk, why do we see so many impact craters in the polar regions which are not aligned with the invariable plane of the solar system? Where did the polar impactors come from? - submitted by Jon Wilcox, Interested public, 09-29-2011

The craters we see on Mercury do not date from the primordial times of accretion. We believe that whatever craters were formed back then have long since vanished, due to subsequent geological processes on Mercury, including volcanism and additional cratering. The craters present today have accumulated on Mercury since the heavy bombardment period about half-a-billion years after accretion (the "Late Heavy Bombardment," about 3.9 billion years ago) until the present. They have been formed by collisions with asteroids and comets, which arrive from all directions.

-Clark Chapman, Southwest Research Institute
MESSENGER Geology Discipline Group

It seems to me that Mercury has more craters per square mile of surface area than either the Moon or Mars. Is this correct, if so, why? Also, does Venus have craters? Thanks, and keep up the good work. --David Stephens

- submitted by David Stephens, Interested public, 09-07-2011

The density of impact craters on a planetary surface varies not only from planet to planet, but also from place to place on a particular planet. For example, the lunar highlands have a higher crater density than do the younger lunar maria.
One factor that may contribute to the impression that Mercury has a higher average crater density than Mars and the Moon is the great abundance of secondary craters on Mercury. Impact velocities on Mercury are much higher, causing larger ejection velocities and thus greater production of distant secondaries compared to the Moon and Mercury. However, for larger than about 100 km in diameter, the crater densities of Mercury and the lunar highlands are almost the same. At diameters smaller than about 100 km, Mercury actually has a lower crater density because extensive volcanic eruptions have covered or destroyed many smaller craters.
Venus only has large craters (diameters larger than about 40 km) because the dense atmosphere helps to protect the surface from impacts. Also, surface processes have erased some older craters. The average surface age of Venus is fairly young (relative to the 4.5 billion year age of the planet), due to the high erosion rate.

--Zhiyong Xiao, University of Arizona and China University of Geosciences
MESSENGER Geology Discipline Group

Re: Image ID: 329264. It seems to me that the small crater, overlying the double ring crater at the ~11 o'clock position, has a floor which exhibits two different ages - going by the number of craters at least, with the area further from the double ring crater appearing younger. At first glance I assumed that contrary to the caption, the smaller crater preceded the larger and had been partially overlaid with impact ejecta from the later event, but this doesn't make sense. The only way I can make sense of the image is if the apparently younger part of the smaller crater floor is the result of a significantly more recent re-surfacing event, presumably a volcanic flood. Is this your view also, and if so do you think it could be associated with the "rille" that extends WSW from the N rim of the larger crater? - submitted by Gilbert Smith, Interested public, 09-02-2011

The smaller crater definitely came after the larger one – it is superposed on the rim of its larger neighbor. If the larger impact had happened more recently, the smaller crater would have been completely destroyed and covered by ejecta. The "rille" is probably a chain of secondary craters, although it's a little hard to tell for sure. Clearly the area has experienced extensive modification by impact processes. It is difficult to know why part of the smaller crater's floor has a slightly smoother appearance. However, much of that area is also in shadow so we don't know what that portion of the crater's floor looks like. It is definitely possible that this area has been affected by volcanism. Both the large crater and the smaller one look to be shallower than we would expect, so they could have been partly filled in with lavas.

--Carolyn Ernst, Johns Hopkins University Applied Physics Laboratory
MESSENGER Geology and Geophysics Discipline Groups

Today's picture 17/8/11 ../Explore/Science-Images-Database/pics/fresh.png shows one fresh crater. The area in the left hand corner has an unusual appearance, in that it looks like a ring of multiple craters, twenty or thirty of them.  An ideas of the origin of this?  Is this a very old crater, that has been the subject of an intense bombardment, and subsequently had its base flooded by lava from the plains to the top, covering the central craters?  But then what. obscured the bombardment craters outside the walls of this old crater? - submitted by John Davies, 08-17-2011

You've made a good observation and your explanation is probably correct. The rim of the crater to which you are referring has been greatly degraded and a number of smaller craters are superposed on the rim. This is probably a remnant of older, more heavily cratered terrain that has been covered in the other parts of the image. For example, to the upper right of the crater is an expanse of smooth plains. This geological unit was probably formed by flooding by volcanic lavas. The smooth plains are lightly cratered, indicating that they formed later in Mercury's history when the flux of bombarding asteroids had declined relative to earlier eras. The interior of the crater may also have been partly flooded, mostly erasing craters of the size that still exist on the rim. The situation in the lower portion of the image is more difficult to decipher. Certainly the fresh 46-km diameter impact crater has deposited a continuous ejecta blanket and pelted the surroundings with secondary craters. But the heavily cratered terrain in this area could have been covered by an episode of volcanism older than that which formed the younger plains to the north.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

what is the nature of the "bluish" hazy streak over a large crater in image id nos 65195,65196, and 65200?? is this an artifact? - submitted by stephen marshall, Interested public, 07-18-2011

What you are seeing in the image is a bright ray from a crater outside the scene crossing an exposure of material with low reflectance. There are several other rays in line with or parallel to the one that crosses over the dark area. Rays form when material ejected from an impact crater strikes the surroundings, crushing and digging up the surface. The fresh material has not been effected by "space weathering" which causes darkening. Thus rays appear as bright streaks extending radially away from the parent crater.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Is anyone doing a comparison of craters to find out what new craters occured since Mariner 10's flybys? Sincerely, Clay Olson, Instructor, Retired (2500 students taught), Santa Cruz City Schools. - submitted by Clay Olson, Other educator, 06-07-2011

Mariner 10 viewed only about 45% of Mercury's surface, at an average pixel resolution of approximately 1 kilometer. Roughly 5 or 6 pixels on crater are needed to clearly recognize it as such.

During MESSENGER's primary mission, plans are to return a global monochrome mosaic (with lighting conditions good for studying surface morphology) that has a spatial resolution of 0.25 km/pixel (250 meters/pixel). Thus, on the part of the planet seen by Mariner 10, comparison with MESSENGER images could reveal any new craters larger than about 5 or 6 km in diameter.

During Mariner 10's third flyby, a few small areas were imaged at higher resolution, a few hundred meters per pixel. Comparison of MESSENGER data with the Mariner 10 high-resolution images could show new craters in the one- or two-kilometer size range.

See also the related Q&A entries here and here.   Thanks for your service as a public school teacher.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What is the biggest crater on Mercury? - submitted by leefontenot, Elementary school student, 05-26-2011

Planetary scientists use the term "basin" for an impact crater larger than about 200 kilometers (120 miles) in diameter. The largest recognized basin on Mercury is the Caloris basin, discovered in Mariner 10 images. It is about 1500 km (930 mi.) in diameter.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hi again, I made the suggestion for a name of the crater called Ring around the Basin, my name suggestion was Doppler. The fellow I was talking about is Albert Franz Doppler (1821 to 1883). He was a composer born in Lemberg, which I believe is in the Ukraine. His brother and father were also composers. Thanks again for your time, I really enjoy the MESSENGER site and check in on it daily.   John - submitted by John Stewart, 05-26-2011

That's a good suggestion for a name. However, there is a lunar crater named "Doppler," for the Austrian physicist (coincidentally, a contemporary of your composer). I believe that the IAU rules prohibit or discourage the use of the same name for features on two different bodies.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I have a suggestion for the yet unnamed basin in photo called "Ring Around The Basin" My suggestion for a name is "Doppler", for double as you well know. Thanks for your time and patience with a novice star gazer. John - submitted by John Stewart, 05-19-2011

The International Astronomical Union's theme for naming craters and basins on Mercury is persons who have made contributions to the arts and humanities. So unless there is a writer, painter or composer named "Doppler", that name won't qualify.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

It appears that all craters that are about 20 miles in diameter and larger have similar depths while, among small craters, depth and diameter appear related. Is this correct? Why? Or, in other words, why aren't larger craters deeper? - submitted by Eliot Long, 05-15-2011

Generally speaking, the greater a crater's diameter, the deeper it will be. However, a crater's depth cannot grow indefinitely: at some point, the material forming the walls of the crater is unable to stand, and the walls collapse into the crater cavity, covering part of the floor and making the crater less deep. The maximum height that a free-standing wall of rock can reach is determined by the strength of the rocks and the planet's surface gravity. Other factors that cause large craters to be shallower relative to their smaller counterparts include rebound/uplift of the floor, the presence of impact melt pools, and infilling with volcanic material or ejecta from nearby large impacts.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

The recent pictures of the landscape of Caloris shows the craters without the common ejecta rays of other impacts, this would suggest to me that the surface may have been "hot" when the impacts occured. The impacting objects looked like they were absorbed rather  than impacting and fragmenting.  Is it possible that the surface of the Caloris Landscape was hot during impact? - submitted by John Stewart, 05-10-2011

Actually, there are many rayed craters within the Caloris basin, as you can see in this stunning mosaic of images from MESSENGER's first flyby. The large, dark-rimmed craters are old enough that their bright rays have faded because of "space weathering" by micrometeoroid impacts and the action of the solar wind.

If an impactor did strike a surface of completely molten rock, the resulting crater might not be preserved for very long because the liquid target would rapidly flow inwards to fill the cavity.

Hypervelocity impacts are quite removed from our everyday experience, such as throwing a pebble into a patch of soft mud. "Hypervelocity" means that the impactor is traveling faster than the speed of sound in the target rocks. The average speed at which asteroids and comets strike Mercury may be as high as 40 kilometers per second (89,000 miles per hour). This is around five times faster than the speed of sound in typical rocks. At these speeds, the target materials can't "get out of the way", leading to almost instantaneous release of the impactor's kinetic energy, vaporization of the impactor and target materials, and production of a shock wave that excavates the crater.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What is the age of the most recent impact crater site on Mercury?  Can and will MESSENGER obtain pictures of any impacts that may occur during its mission time around Mercury? Thanks again,John - submitted by John Stewart, 05-03-2011

Without a sample in hand that can be dated by radioisotope techniques, geologists use other criteria to date a particular surface feature.

 An old surface will have accumulated more craters per unit area than a young surface. Crater size-frequency distributions are an important tool in judging the relative age of planetary surfaces.

A younger impact crater will have a sharper appearance than an older crater, because its walls and ejecta have not been worn down by the rain of smaller impacts. Crater rays fade with time because of the effects of mixing and "space weathering" by impacts of all sizes. So young craters have bright rays. Based on these criteria, Kuiper, Hokusai and Debussy are among the youngest large craters on Mercury. There are many many smaller craters that are younger than these examples.

The highest resolution images that MESSENGER will obtain are about 10 or 15 meters per pixel. Thus in these images the smallest crater that can be resolved might be 60 or more meters in diameter. If an area is imaged at high resolution at two different times during the mission, researchers can look for the presence of a new impact.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Not so much a question - since craters on Mercury are named for writers, artists etc., The photo recently published of an "X.html" of secondary craters. Could it be named for Robert Louis Stevenson for his "Treasure Island"? It might be appropriate. I hope it will be suggested to the IAU at their next session for naming features. - Mickey Schmidt, Retired Planetarium Director.  - submitted by Mickey Schmidt, Other educator, 04-29-2011

That is a clever suggestion. The name "Stevenson" has not yet been used on Mercury or on any other planetary body. We will keep this in mind and may include your suggestion in our next proposal to the International Astronomical Union.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I am facinated by the MESSENGER project. Kudos to all who make it work. The most recent picture as of 4/19 shows a crater at the top. At my age, I may be the only one who noticed the crater appears to be similar to those incredibly annoying smiley faces with a big grin and a winking eye as in ;-).     Best to all!! Ted Whittington,  Elgin, IL - entered by Q&A admin, 04-22-2011

Planetary landscapes are endlessly fascinating. Perhaps psychologists could use MESSENGER images instead of inkblots for Rorschach testing. Since you see a smile, I can deduce that you are a happy, well adjusted, intelligent person (like all fans of space exploration).

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Congradulations team. What a monumental success. Questions. A. Given high velocities, can impact sites be expected to yield large crystals? B. Would crystalline forms be expected / observed /observations within the camera or assay devices aboard? C. I am curious about cave or hollow structure within deep impact regions. Does the team have any insight as to best investigate a fissure (hence sealed or overburden?) D. Given the expectation of a highly dense ferrite core, are the magnetic poles expected to be similar....or different than terra firma.   Regards, a Johns Hopkins alum


- submitted by mark mcgary, Interested public, 04-15-2011

A & B. Rocks are made of minerals. A mineral is a solid inorganic compound with a specific chemical composition whose atoms are arranged into a regular geometric pattern, that is, a crystal structure. On planetary bodies like the Moon and Mercury, the surface is composed of igneous rocks - rocks that formed from melted material. If a melt cools slowly, there is more time for the atoms to arrange themselves into a crystal form, and hence crystals can grow larger. A melt that cools rapidly will have very tiny crystals, or may even be all or partly glassy, i.e., lack a crystal structure because the atoms didn't have time to arrange into a regular structure. During the formation of an impact crater, some of the target rocks may be melted. For example, impact melt ponds have been observed on the interiors, walls and rims of lunar craters. Small splashes of melt will cool quickly and "quench," yielding small crystal sizes. A very large, thick impact melt pool could cool more slowly, and so the resulting rocks would be expected to have a larger grainsize. Geologists use a petrographic microscope to examine slices of a rock that have been polished thin enough to transmit light. Study of the texture and grainsize of the minerals in a rock gives clues to its origin and history. MESSENGER will provide information on the mineral make-up of Mercury's rocks by measuring reflectance spectra (detailed color information) for comparison with lunar and other samples. MESSENGER's Neutron, Gamma-ray and X-ray spectrometers will provide information on the elemental (atomic) make-up of Mercury's surface, for comparison with the chemical composition of various mineral types. Major rock-forming igneous minerals on the Earth, Moon, Mars, and asteroids include feldspar, pyroxene, and olivine.

C. Impact cratering produces holes in the ground. Smaller craters on Mercury (less than about 3 kilometers in diameter), have a simple bowl shape. Larger craters have flat floors, and the walls can collapse by oversteepening to form terraces on the walls. Central peak mountains are formed when deep-seated material rebounds from the shock of the impact. While impacts can produce intense fracturing of the target material, the great pressures involved would not be expected to leave any caves or other voids intact. Curiously, some impact craters on Mercury have pits in their floors. However, the pits are probably the result of volcanic activity that took place well after the crater formed.

D. Read about Mercury's iron core, and find out about the magnetic field here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Can you name a discovery on Mercury after me? perhaps a mountain or crater? My Name is Atom, I would greatly appreciate it. Thank you Atom Charles


- submitted by Adam, Interested public, 04-14-2011

Well, we can consider it, but you would have to be dead first. It is the International Astronomical (IAU) Union that is in charge of assigning official names to features on Solar System objects. The IAU's theme for naming craters on Mercury is persons who have made major contributions to the arts and humanities. Political or religious figures are prohibited. The person's contributions must have been considered to be important for at least 50 years, and the person needs to have been deceased for at least 3 years before the name is submitted for approval.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Aside from the Caloris Basin impact, are the density and distribution of cratering on Mercury within the predicted range for a planet of its size, nature, and orbital location? - submitted by Ralph Ricketson, Interested public, 04-09-2011

Mercury has more two-ring impact basins than does the Moon. This must result from Mercury's particular combination of factors (gravity of the target body, strength of the material in which a crater forms, impactor size and speed) that control the size and morphology of impact craters.

At certain size ranges (less than about 25 km diameter) Mercury has a lower density of impact craters than does the Moon. This is likely a result of the extensive eruption of volcanic plains on Mercury, which covered many craters. Also, for reasons that are not well understood, secondary craters produced by primary impacts are more abundant on Mercury than on the Moon.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why does it seem everything on Mercury is named after the Japanese? Did a Japanese astronomer discover Mercury? from JBurrs - entered by Q&A admin, 04-08-2011

Mercury is one of the five planets that have been known as long as humans have been looking at the sky (Mercury, Venus, Mars, Jupiter, Saturn).

The International Astronomical Union's theme for crater names on Mercury is people who have made important contributions to the arts and humanities (e.g., writers, poets, composers, painters). You can see all the IAU approved crater names on the U.S. Geological Survey's nomenclature website.

I just did a quick check for a few countries, and here are the number of crater names from each:

Japan 23   USA 16   Italy 21    England 14 France 29     China 17

--David Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

I recently viewed the Equator to Pole pictures from the MESSENGER mission to Mercury, I noticed that all the impact craters had some fallout from high speed collision. But what was different was the impact site to the left of the big crater. It appears to have what looks like a smoke plume going out in two directions, perhaps the object that hit the surface was burning for some time after impact. Please let me know what your staff thinks of the black plumes from the crater.
I have the MESSENGER site loaded up to my favorites, I have been waiting for pictures since the launch back in 2004 - 2005.   Thanks for your time, John in Canada - entered by Q&A admin, 04-08-2011

You are referring to Matabei crater. It has certainly attracted a lot of attention. Have a look at answers to three previous inquiries: here, here, and here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why do all the craters seem to be so round instead of jagged edged like on other bodies in the solar system? Looks like bullets hit Mercury. from JBurrs. - entered by Q&A admin, 04-08-2011

Impact craters on the solid bodies of our Solar System are produced in "hypervelocity" collisions. This means that the comet or asteroid striking the surface is traveling faster than the speed of sound in the target material. Typical impact speeds on the Moon are about 20 kilometers per second (km/s) and may be higher than 40 km/s on Mercury. Note that 20 km/s is about 45,000 miles per hour, much much faster than the speed of a bullet leaving a rifle. The tremendous kinetic energy of the impactor is released almost instantaneously, and results in the excavation of the crater. Nearly all impact craters on all the planets and moons have circular rims, unless the impactor struck at a low angle (less than about 30 degrees above horizontal). Impact angles below 30 degrees produce elongated crater forms.

The appearance of the surface of an airless body like Mercury or the Moon is strongly affected by the lighting conditions. Low-angle lighting (with the Sun low on the horizon) produces long shadows and emphasizes the texture and topography of the surface. This could cause the "jagged" appearance to which you refer. If the Sun is more nearly overhead, there are few shadows and variations in the inherent brightness of the surface dominate the appearance.

Have a look at these two image sets that illustrate the effect of lighting on the appearance of Mercury's surface: here and here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Can someone tell me what is casting a shadow left of big crater in the following picture?? Thank You. Marc Winkelman
- entered by Q&A admin, 03-31-2011

You are referring to the first color image from orbit. The caption to the single-band (black and white) version mentions the feature that attracted your attention. It is the unusual dark-rayed crater Matabei. This crater was also the subject of image releases in 2008 and 2010.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

 I was looking at the first photo from MESSENGER of Mercury's surface when I noticed an interesting feature west of Debussy. It is the darker, slightly blue inverted V that I am referring to. To me it looks like the same object it casting two shadows from two different light sources but I know that is highly unlikely. Is this a known structure? I am curious as to what it is. Brian Palmer, On. Canada.

You are referring to the first color image from orbit. The caption to the single-band (black and white) version mentions the feature that attracted your attention. It is the unusual dark-rayed crater Matabei. This crater was also the subject of image releases in 2008 and 2010.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Discounting the first answer tossed out about the "Dark Ejecta" of Matabei ... if Mercury were a moon located elsewhere in the colder part of the solar system ... some folks would be thinking: evidence of ancient volcanic activity ... that hole appears to be about 2000M deep.   - submitted by psdave, Interested public, 03-30-2011

Volcanism is one of the fundamental geologic processes that modifies the surfaces of solid-surface bodies throughout the Solar System. Silicate volcanism is important on Mercury, Venus, the Earth, the Moon, Mars, the asteroid Vesta, and Jupiter's moon Io. "Cryovolcanism" involving water, ammonia, methane, or other volatile compounds has taken place on some of the icy moons of the giant planets in the outer Solar System.

There has been extensive volcanism on Mercury, and we have had over 40 image releases related to the topic.

For Matabei, however, the current consensus view on the MESSENGER science team is that the best explanation of the dark streaks is that they were deposited as ejecta from an impact crater. We will be getting additional data for this feature in the coming year. Topographic measurements derived from Mercury Laser Altimeter data and stereo images will allow the shape of Matabei (and all of Mercury's surface) to be better understood. Images with differing lighting conditions will enable further assessment of the feature's characteristics. All that new information could reinforce the hypothesis that it was formed by impact, or instead could shift our interpretation to some other process, potentially volcanism. Review and consideration of evidence and testing of hypotheses are what science and exploration are all about!

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Congratulations on your progress with MESSENGER to date. Being on the verge of discovering that of which we were entirely ignorant is a very exciting time!

Do we already know why (it would appear) the vast majority of Mercury's craters are circular in shape? Hardly an oval-shaped crater can be seen in the images I have looked at so far. Up to now I have assumed that a fairly vertical impact would be required for a circular crater. Given that Mercury has no atmosphere with which to slow incoming matter I could only imagine a few things that might explain the predominance of circular craters: 1) there was a dense atmosphere present when most of the craters were formed, 2) Mercury wasn't always located in its present position, 3) Mercury is extremely dense and has a high gravity for its size, 4) Mercury's surface is "sticky" and at least somewhat elastic.

I would love to hear the real reason for the predominance of circular craters on Mercury. - submitted by Robert Rogers, Interested public, 03-30-2011

You have made a good observation. Similarly, nearly all craters on the Moon are circular. This puzzled early lunar telescopic observers, who also thought that impacts would have to be nearly vertical to produce circular craters. However, we now have a better understanding of the physics of hypervelocity impact cratering, both from theory and from laboratory experiments ("hypervelocity" means that the impacting body is traveling faster than the speed of sound in the target rocks.) Under these conditions, the energy of the impactor is released nearly instantaneously in an event similar to an explosion. It turns out that most impact angles will produce a circular crater; an impactor must approach on a path making a very shallow angle (less than about 30 degrees above horizontal) in order for the resulting crater to be elongated into an elliptical shape. However, oblique impacts at angles over 30 degrees will produce asymmetrical ejecta patterns though the crater is circular.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

If you look just slightly right of centre in this image there appears to be a crater with two perpindicular trenches running from it. Is this an image artifact or a process that I am not familiar with?

Question from Nigel Lavery, South Africa - entered by Q&A admin, 03-02-2011

The surface of Mercury in the image you have selected is wonderfully complex. The texture and topography within this scene are emphasized by the lighting conditions. The Sun was relatively low on the horizon as MESSENGER passed this part of Mercury on its first flyby of the innermost planet (January, 2008). As a result, surface features cast long shadows, highlighting slight differences in elevation.

In the lower right (southeast) corner is a gigantic curved cliff, part of the very large "Beagle Rupes" structure. This rupes (fault scarp) likely formed as Mercury's interior cooled and contracted, thrusting part of the crust up and over an adjacent section.

I suspect that the trench-like features you have identified were formed by two causes. First, there may be small scarps that are casting shadows; these may have an appearance suggestive of a trench. Second, chains of secondary craters are present in this image. Such chains arise when the formation of a larger ("primary") impact crater causes chunks of material to be thrown out of the growing crater cavity. Sometimes these chunks can strike the surface near the primary crater, producing chains of secondary impact craters extending in a line radially away from the primary. The secondary craters may partially overlap, forming a long valley-like depression.

The MESSENGER science team is always glad to know that the mission is generating interest among members of the global public. We look forward to sharing more of our findings as the pace of discovery quickens once the spacecraft enters orbit around Mercury in late March, 2011.

--David Blewett, Johns Hopkins University Applied Physics Lab

MESSENGER Participating Scientist

Volcanism, tectonic faults, rock types and other topics related to the surface of the planet

I have a homework assignment that I am doing for my Astronomy class. And the question for the assignment is What are the three pieces of evidence that water exists in permanently shadowed polar craters on Mercury? If any one can help me out or let me know references I would greatly appreciate it. Thank you. - submitted by Vito Palmisano, College student, 04-22-2016

You can start by looking at the list of Top Ten Science Results from MESSENGER, and scrolling to #2.

Here are some references:

Lawrence, D. J. et al., Evidence for water ice near Mercury's north pole from MESSENGER Neutron Spectrometer measurements, Science, 339, 292-296, 2013.

Neumann, G. A., et al., Bright and dark polar deposits on Mercury: Evidence for surface volatiles, Science, 339, 296-300, 2013.

Paige, D. A. et al., Thermal stability of volatiles in the north polar region of Mercury, Science, 339, 300-303, 2013.

Chabot, N. L., et al., Craters hosting radar-bright deposits in Mercury's north polar region: Areas of persistent shadow determined from MESSENGER images, Journal of Geophysical Research: Planets, 118, 26-36, 10.1029/2012JE004172, 2013.

Chabot, N. L., et al., Images of surface volatiles in Mercury's polar craters acquired by the MESSENGER spacecraft, Geology, 42, 1051-1054, 2014.

Harmon, J.K., and Slade, M.A., 1992, Radar mapping of Mercury: Full-disk images and polar anomalies: Science, v. 258, p. 640–643, doi:10.1126 /science .258.5082.640.

Harmon, J.K., Slade, M.A., and Rice, M.S., 2011, Radar imagery of Mercury's putative polar ice: 1999–2005 Arecibo results: Icarus, v. 211, p. 37–50, doi:10.1016/j.icarus.2010.08.007.

-- Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

At this point in time what have we been able to deduce from the images from the MDIS about what elements make u the surface of Mercury? - submitted by Lilli Helps, College student, 06-29-2015

The MDIS camera takes pictures of the surface in reflected sun light. The Wide Angle Camera (WAC) has a filter wheel that allows images to be collected in 11 different colors (wavelength ranges or bands) in the visible and near-infrared (NIR) portions of the electromagnetic spectrum. Because different materials have different colors, some limited information on the composition of the surface can be obtained from analysis of the amount of light that the surface reflects in each wavelength band. This information can be more or less detailed depending on the particular surface and the number of wavelength bands that are available. Mercury's surface lacks diagnostic absorption bands in the visible-NIR, so while the WAC data can be used to map out terrains with different color characteristics, no direct information on the mineralogical or elemental composition of the surface is obtained from the WAC.
MESSENGER did carry three instruments that do provide measurement of the chemical elements that are present in the surface: the X-Ray Spectrometer (XRS), the Neutron Spectrometer (NS), and the Gamma-Ray Spectrometer (GRS). Like Venus, the Earth, Moon, Mars, and most asteroids, Mercury's surface is made of silicate rocks, which are composed of minerals (compounds) of silicon, oxygen, aluminum, calcium, and magnesium. Curiously, Mercury's surface rocks are very low in iron, despite the planet's large iron core. MESSENGER's instruments have found that the surface has a surprisingly high content of volatile elements such as sulfur, potassium, and sodium. Prior to MESSENGER, it was expected that these elements would be depleted because it was thought that Mercury's formation involved high-temperature processes that would have depleted volatile elements. In fact, these discoveries about Mercury's composition were listed as the #1 top science result of the mission.

-Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Is it conformed if there is any separated rock or even dust on the surface of mercury ? - submitted by Abdalla Jaber, Interested public, 05-13-2015

Images with sufficient spatial resolution show that boulders are present on the floors and near the rims of some impact craters on Mercury. To see examples check these three links: this one, here, and here. If more detailed images were available, many more examples of boulders would no doubt be found. For example, the Lunar Reconnaissance Orbiter Camera obtains images of the Moon's surface at much finer spatial scales than was possible for Mercury with MESSENGER, and boulders are often seen in LROC images (such as here).
The surfaces of airless bodies are subjected to continuous bombardment by solid particles that range in size from nanometer-scale up to asteroids or comets that are kilometers in diameter. This pounding produces a surface covered by broken-up rock that planetary geologists call "regolith". The regolith consists of material from boulder size to fine, powdery dust. Mercury receives a greater flux of impactors than does the Moon, and these impactors are traveling at higher speeds. Studies of the way that Mercury's surface reflects light suggest that the average particle size of Mercury's regolith is smaller than that on the Moon. From samples returned by the Apollo astronauts and Luna robots, it is known that the average particle size of lunar soil is about 70 micrometers.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I need to find out if a large crater of 80 km in diameter, what is the length of the scarp? - submitted by Heather Clynes, College student, 04-25-2015

The word "scarp" is used by geologists to mean a cliff. In particular on the planet Mercury, scarps are formed by compressive forces within the crust that cause one section of rock to be pushed up and overtop of another along a thrust fault. Small scarps of this kind have also formed on the Moon; this link has an illustration of such a thrust fault and scarp.
On Mercury, impact craters are sometimes cut and deformed by scarps, as can be seen in this image in the MESSENGER Gallery.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I read at, that there is enough hidden ice in Mercury's polar craters, to cover Washington (presumably state, not DC, though not specified which) more than two miles thick. Is this amount correct? Ca. 600,000 km^3? If so, then perhaps even Mercury might have some biological potential, especially if there is any geothermal heat. - submitted by Tatiana Covington, Interested public, 04-23-2015

Analysis of data from MESSENGER's Neutron Spectrometer related to the abundance of hydrogen in Mercury's polar regions was reported in a paper by David Lawrence and colleagues in the journal Science in 2013 (volume 339, pages 292-296). The data are consistent with hydrogen (in the form of water ice) within permanently shadowed craters at the north and south poles. The presence of water ice within permanent polar shadows has been suspected since Earth-based radar measurements in the 1990s that found that polar craters have unusual radar reflectivity that is suggestive of ice. Additional evidence for ice in polar craters comes from models of the temperatures within the shadowed polar craters (indicating that water ice should be stable over billions of years), and measurements of the reflectivity of crater interiors by the MESSENGER laser altimeter. The reflectivity maps show areas of high and lower reflectance that can be explained by the presence of surface frosts in some areas, while other areas are covered by dark material, likely to be carbonaceous matter delivered by the same comet and asteroid impacts that brought the water.
The paper by Lawrence and colleagues estimated that the total amount of polar ice is in the range 2.1 × 10^16 to 1.4 x 10^18 grams. One gram of ice has a volume of about 1 centimeter cubed, so you can compute for yourself the thickness that this amount would reach if placed uniformly over a given area.
With both water and organic material present, Mercury's poles would be an interesting place to study pre-biotic material and the history of the delivery of water and organics to the inner solar system.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

With the understandable excitement over discovering water on Mercury, I have lost touch with the issue of iron in the regoliith. Is there now a definitive answer to this question? How much iron do we find in Mercury's surface? Thank you. - submitted by Bryce Johnson, Journalist, 04-02-2015

The most recent comprehensive assessment of the abundance of iron in Mercury's surface is a paper by Shoshana Weider and colleagues, published in the journal Icarus (volume 235, pages 170–186) in 2014. From analysis of data from MESSENGER's X-Ray Spectrometer, she concludes that the average iron content of Mercury's surface is about 1.5% by weight. The paper also suggests that the iron exists in sulfide phases (like troilite, niningerite, daubréelite) and as native metal, rather than within silicate minerals. The iron abundance on Mercury is very low compared to the Moon, where the highlands contain about 3-4 wt.% iron and the iron content of the dark, volcanic maria is approximately 14 wt.%. While lunar materials do contain some native metallic iron, mostly the iron is in the ferrous form, within silicate minerals like pyroxene and olivine.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Are there any caves on Mercury, and if so how large are they? - submitted by Frank Parsons, Middle school student, 03-30-2015

There might be lava tubes, or voids related to impact melts or formation of hollows.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I do not fully understand low reflectance material (LRM) what is it's relavance to MESSENGER? - submitted by Ellen, College student, 02-16-2015

Low reflectance material (LRM) refers to a rock type that is exposed at some places on the surface of Mercury. The LRM is one of the major categories of material that have been defined based on MESSENGER's global imaging of the planet. As its name implies, the LRM has lower reflectance (that is, it is darker) than other mercurian terrains. The LRM can be seen in the global views shown here. In addition to being darker than the typical surface, the LRM has color properties that are described as "bluer" than other rock types. This color characteristic is emphasized in the enhanced-color images that have been produced by applying statistical techniques to MESSENGER MDIS eight-color images. In such an enhanced-color view, the LRM appears as shades of deep blue.
The LRM is often exposed by impact craters (like Basho), indicating that in some cases it originated in Mercury's interior. It is also interesting that hollows appear to form preferentially in the LRM. By considering the color data along with maps of chemical abundance obtained by the MESSENGER X-Ray Spectrometer, scientists are trying to figure out what particular mineral phase causes the LRM to be dark.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hello MESSENGER team. I have a question to ask you regarding the planet Mercury. In artist and computer renders, the planet appears brown in color, but in the images captured by Mariner 10 and MESSENGER the planet is grey all over. What color is the surface of Mercury: is it grey, brown, or some other color? And if it IS grey, as I do believe it is, why do so many sources show Mercury as a brown rock?
- entered by Q&A admin, 11-02-2014

Many of the images shown in the MESSENGER project's Image Gallery were taken through a single filter that passes a relatively narrow range of wavelength (color) of light. When such an image is displayed on a computer monitor, it is represented by 256 levels of grey between pure black and pure white.

In other cases, the MESSENGER Wide-Angle Camera (WAC) obtains images of the same portion of the planet through as many as 11 different wavelength filters. Throughout the mission, such sets of color images have provided information on the global, regional, and local reflectance properties of the surface. These data, along with more detailed reflectance spectra from the MASCS Visible and Infrared Spectrometer, show that Mercury has only very subtle color variations. Mercury's surface does reflect more light at the longer-wavelength (red) end of the spectrum than at the shorter-wavelength (blue) end, hence to the human eye Mercury would probably appear somewhat brownish grey.

By displaying three of the WAC color filter images though the red, green, and blue channels of a computer monitor, it is possible to produce an image that approximately depicts the "true color" of the surface as it would appear to the human eye. Similarly, the contrast of a three-filter set can be enhanced to emphasize the color differences (and hence compositional differences) associated with various surface features. Examples of "true color" and enhanced color images can be found in the Image Gallery; here is one hemispherical view.

You can also search the MESSENGER Q&A page for "true color" to find some previous questions related to this topic.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

[1] Why is there more craters on some parts of Mercury than others? [2] I have heard that volcanic activity is to blame for this. Why would that cover such large portions of the planet? - submitted by Kitty S., Middle school student, 10-28-2014

Impact cratering is a ubiquitous geological process that has affected all solid bodies in the Solar System through time. There are a variety of reasons that one part of a planet's surface might have fewer impact craters than another part. On the Earth, there are many active agents that have eroded or covered impact craters. These include the action of flowing water, moving ice sheets, and the wind. Volcanic eruptions also modify the landscape by burying pre-existing features with lava or ash deposits. "Flood volcanism" has covered large areas of the continents. Examples include the Columbia River basalts in northwestern North America and the Deccan Traps in India. And of course the sea floor is continuously formed by volcanic eruptions along the mid-ocean ridges, making the sea floor much younger than the continents.
On airless bodies like the Moon or Mercury, wind, water and glaciers have not played a role in changing the landscape. But impact cratering and volcanism have profoundly modified the surfaces of these bodies. When a large impact occurs, it throws out huge quantities of material that was in the target location. This ejecta covers the crater's surroundings to varying degrees. Thus, the ejecta-covered surface visible after a big impact will have fewer craters per unit area than did the pre-existing surface. Similarly, flood volcanism has covered large portions of both the Moon and Mercury. The lunar maria (Latin for "seas") are the dark, smooth areas that we see on the near side of the Moon. These areas appear smooth because they were formed by flood lavas that covered pre-existing craters. (The brighter parts of the Moon, the highlands, are more rugged because they have not been covered by lava, and hence retain older craters than do the maria).
On Mercury, the "smooth plains" are equivalent to the Moon's maria: vast areas that were covered by volcanic lavas. In the case of Mercury, the Moon, and Earth, the energy to partially melt rocks deep in the interior comes from the decay of naturally occurring, long-lived radioactive elements like potassium, uranium, and thorium. The molten rock (magma) is less dense than the surrounding solid rock, and thus in many cases is able to rise to the surface and erupt. Gentler eruptions produce lava flows; magma containing a lot of dissolved gas may erupt explosively and produce pyroclastic ("ash") deposits. The chemical composition of the lava (mainly its silica content) controls the viscosity of the lava (that is, how "runny" it is). The flood lavas that erupted on the Moon and Mercury were highly fluid - this helped them to flow long distances and cover large areas.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

It's amazing how Mercury could be deposits of ice in areas of permanent shadow. When this world is too near the Sun. No doubt this is weird, but possible, giving rise to many questions about the possibility to exist in your sub. Soil deposits unfrozen water, a hypothesis to be considered by the investigators, even a very remote possibility in credible. Has another aspect, despite Mercury being constantly bombarded by intense solar radiation,, it may contain certain elements, such as metals and crystals, in various forms, which may actually be useful to man and Industry, mainly in its sobsllol. This hypothesis should be viewed, analyzed. Mercury has Unique features in our Solar System, being a planet that is essentially under the action of the gravitational field of the sun, not to mention the intense radiation that bombards the planet because it is too close to the Sun. The Departure seems to be a world completely without any chance of Sterile Organic contain elements due to its proximity to the Sun, but the latest investigations that have been made, so why is not found something that can be dry ice, or something similar. Hopefully soon to have more concrete results of the discoveries made in Mercury. - submitted by Luiza Martins, 10-23-2014

The idea of ice existing in areas of permanent shadow was first proposed in the early 1960s (for polar craters on the Moon). The first evidence for polar ice on Mercury came from observations using Earth-based radar in the early 1990s.
New evidence for water ice in Mercury polar shadows came from MESSENGER in 2012: neutron spectrometer measurements of enhanced hydrogen abundance, laser altimeter detection of bright spots in polar craters that is likely to be surface frost, and thermal modeling that shows that the temperatures in the polar permanent shadows are right for water ice to be stable for long periods of time.  Refer to this previous question for more about those results.

The recent publication of MDIS images that use long exposures to provide a view within areas of shadow are yet further evidence that water ice exists in these locations. The majority of the evidence suggests that the material in the polar shadows is water ice, rather than some other compound. For example, if the material was carbon dioxide ice (CO2), then there would not be a hydrogen enhancement as is observed by the MESSENGER neutron spectrometer.
On Earth, many useful deposits of metals (ore deposits) were formed by hydrothermal processes, involving extensive chemical reactions in the subsurface by heated water flowing through pore spaces and fractures. Mercury is very unlikely to have abundant liquid water in the subsurface. However, some interesting chemistry may be taking place between ice in the permanent shadow and the host rocks and soils. In fact, in shadowed locations that are just a bit too warm for water ice to be stable on the surface, MLA and MDIS find evidence for the presence of dark carbonaceous compounds, likely delivered by comets.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Absolutely love the shadowed polar crater images released today on the MESSENGER site. Looks like the results are excellent, a lot of detail is visible on the permanently shadowed floors, including the smoother patches corresponding with detected ice deposits.

The MDIS team has been planning long-exposure images to attempt to see into the shadowed portions of polar craters for quite a while, and it is gratifying to obtain useful results. The observations of north polar craters are only possible with the broadband ('clear') filter of the WAC: it passes enough light to get a good image using exposure times that are short enough to avoid major smear from motion of the spacecraft. The WAC clear filter is centered at 700 nm and has a width of 600 nm. As you mention, the camera field-of-view (FOV) is moving rapidly across the surface when the spacecraft is over high northern latitudes, and thus smear is a major concern. The NAC obtains images through a filter with a width of 88 nm centered on 750 nm, and hence the amount of light passed is not sufficient to get good signal without extensive amounts of smear that result in an effective spatial resolution worse than obtained with the WAC clear filter.
Several attempts have been made to obtain NAC images within Chao Meng Fu, near the south pole. Here the motion of the FOV is not enough for smear to be a problem, so imaging within the shadows may be possible with the NAC. However, the attempts so far have not yielded useful images of the area in shadow. The MDIS team will make additional tries under different indirect illumination conditions in the hope that the floor of Chao Meng-Fu will give up its secrets.

--Dave Blewett, MESSENGER Participating Scientist and Nancy Chabot, MDIS Instrument Scientist
Johns Hopkins University Applied Physics Laboratory

Regarding hollows, are there any estimations for how deep they are? The images suggest they are shallow, but it its difficult (at least for this layman!) to tell a vertical distance based on pixel resolution. Thanks again! - submitted by Bryce Johnson, Journalist, 07-09-2014

Yes, there are measurements for the depth of hollows. To do this, we use knowledge of the angle of incidence of the Sun's rays, and measure the length of a shadow cast by the rim of a depression in the hollows. Using simple trigonometry, we can calculate the vertical height of the feature.

A paper published in the journal Science in 2011 by MESSENGER science team member David Blewett and colleagues describes shadow-length measurements for hollows in the floor of the Raditladi basin. Those workers found an average depth of 44 meters. This is consistent with some of my recent findings for hollows in higher-resolution images obtained at low altitudes. Here, the hollows' depths seems to be clustered between 10 m and 60 m, with most having depths of about 20 m.
--Amanda Stadermann, Johns Hopkins University Applied Physics Laboratory
MESSENGER summer intern

Talking of the MLA, are there actual profiles available of the more interesting features like the Caloris Basin, Raditladi, Rachmaninoff, the Caloris volcanic features, etc?? Andrew Brown, Kent, UK. - entered by Q&A admin, 06-26-2014

There are multiple MLA profiles through Caloris Basin (many dozens), Raditladi (about a dozen), Rachmaninoff (about a dozen, and additional profiles through the volcanic vent to the northeast of Rachmaninoff), and volcanic features inside of Caloris, including at least one through the 'kidney-shaped depression'. In addition to topographic profiles from MLA, MDIS images can often be used to measure topography from stereogrammetry. In this way, topographic measurements can be made of features in Mercury's southern hemisphere, which because of the spacecraft's highly elliptical orbit, is beyond the range of MLA.

Carolyn Ernst, Johns Hopkins University Applied Physics Laboratory
MLA Deputy Instrument Scientist

I am wondering just how many volcanic vent features have been identified on Mercury. I know of three, but I'm sure more have been discovered. Also, are the ground areas around them all showing the same chemical signatures, or are there differences? Thanks! - submitted by Bryce Johnson, Journalist, 06-23-2014

In response to your first question, so far, 51 confirmed volcanic vents have been identified. However, there is an ongoing search for such features, and there are another approximately 90 vents that have been found by the most recent survey. If you want to read more about it, there was a conference presentation about this in March 2014 that is summarized in this abstract.

In terms of your second question, yes, the volcanic deposits do appear to have a different composition than the surroundings. Unfortunately, MESSENGER's primary instruments for measuring elemental chemistry (the X-Ray Spectrometer and the Gamma-Ray Spectrometer) both view a very large portion of Mercury's surface for any given measurement, and so it is difficult to isolate just the relatively small pyroclastic deposits that surround the volcanic vents. Despite the challenges of this coarse spatial resolution, MESSENGER was able to measure the largest pyroclastic deposit (named NE Rachmaninoff) using the X-Ray Spectrometer. These data show that the area surrounding this volcanic vent has lower amounts of sulfur than does Mercury on average, which is very interesting. Again, this is a very new finding (which you can read more about here), and so the team is still working on interpreting what exactly this means about the origin of this volcanic material, but it is a very exciting finding nonetheless!

Thanks once again for your interest Bryce, and let us know if you have any further questions!

Tim Goudge, Dept. of Geological Sciences, Brown University
MESSENGER Geology Discipline Group

Thinking about the small axial tilt... Could it be geometrically possible for volatiles to exist in geological timescales (even if in much smaller quantity) not only on polar regions, but on the faces opposite to the hemisphere they are of low craters just a few 5 or 10 degrees from the equator of Mercury? If so, could it be tested in the same fashion you did with the former? Thanks in advance, excuse me if it's been asked before. It's admiring all the work you're doing unveiling this underrated planet for us. - submitted by Jesus Cuenca Monclus, Interested public, 05-09-2014

The lowest latitude location observed in Earth-based radar observations that shows evidence for ice is at about 65°N latitude. This may indicate that ice would not be stable at lower latitudes, either due to the lack of permanent shadows at lower latitudes or due to the thermal conditions at lower latitudes even if shadowed. The specific topography of a region will determine where permanently shadowed regions exist; perhaps small scale regional slopes or other features can create small regions of permanent shadow at lower latitudes. Detailed mapping of regions of permanent shadow has not been done below a scale of ~500 meters for Mercury, and even then it has focussed on the polar regions. Additionally, thermal models of the stability of volatiles has not been done outside of the polar regions for Mercury. Having permanent shadows as close to the equator as 5 or 10 degrees may be challenging, but understanding the lowest latitude permanently shadowed regions is an interesting topic and one worth investigating!

--Nancy Chabot, Johns Hopkins University Applied Physics Laboratory
MESSENGER MDIS Instrument Scientist

Many of the images returned from MESSENGER have shown a surprising number of volcanic vent features. Often, they have nearly pristine appearance and seem to be 'recent' in origin. My question is: What do we mean by 'recent'? Within the last million years? Hundred million? More to the point, have we seen any such features believed to have occurred within historical times, say, the last ten-thousand or hundred-thousand years? Thanks again! - submitted by Bryce Johnson, Journalist, 04-18-2014

Hi Bryce, Thanks for the question about the volcanic vent features on Mercury - it is a very good one (albeit difficult to answer!). I agree with you that many of the volcanic vents have a pristine appearance. However, that observation alone does not permit us to ascribe an actual date to the features. The best we can say at the moment is that they have been active in the last few BILLION years (rather imprecise, I know).

Determining the age of any small feature on a planetary body is always difficult. One method employed to estimate relative ages of the volcanic vents is to use the fact that the majority of them are found within impact craters. We can then use the age of the impact crater as an upper limit on the age of the volcanic vent - because no vent within an impact crater can be older than that impact.

From some detailed morphologic work, we can tell that the host craters fall into a range of age categories, between about 4 billion and 1 billion years old. It turns out that we see no vents hosted in craters that fall into the youngest age category (less than one billion years old). This does not necessarily mean that no vents have formed in the last billion years. This is because the method we used for determining the ages of the craters only provides an upper, not a lower, age limit. The youngest crater in which we have identified a volcanic vent is in the 3.25 to 1 billion year age category, which means that the volcanic activity occurred more recently than about 3.25 billion years ago. Currently we are just not able to be more precise concerning the age of the volcanism. However, with more data and more people working on the problem we will make progress toward improving the age estimates. Hopefully this has helped answer your question at least a bit, and thanks a lot for your interest!

--Tim Goudge, Dept. of Geological Sciences, Brown University
MESSENGER Geology Discipline Group

There has been a long standing question about iron on Mercury's surface. How can such a dense planet (5.54 gm/cm3) have so little iron on it's surface? This question pre-dates MESSENGER's orbital mission, so I am wondering if we have revised figures for surface iron from new data. Thanks! - submitted by Bryce Johnson, Journalist, 04-17-2014

The most recent values for the iron content of Mercury's surface were published by Shoshana Weider and her colleagues in a paper in the journal Icarus. She analyzed data from MESSENGER's X-Ray Spectrometer data and found that the average surface has about 1.5 weight percent iron oxide (FeO). As you note, this is very low by the standards of other planetary bodies. For example, most lunar highland rocks contain about 6 wt.% or more FeO, and the lunar maria can have over 20 wt.% FeO. The very low iron abundance in Mercury's rocks suggests the the planet formed under chemical conditions that were extremely reducing, causing nearly all the iron to be in the metallic state (rather than the Fe+2 state of iron in silicate rocks). The dense metal was efficiently drained to the core, leaving a crust and mantle that are bereft of iron.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

It seems every high-resolution image we are getting has at least some 'hollows' in it. So let's turn an earlier question around and ask: Are there any terrains on Mercury that are noteworthy for NOT having hollows? - submitted by Bryce Johnson, Journalist, 04-04-2014

Most hollows are found in the "low reflectance material (LRM)", one of the major color-compositional units on Mercury's surface. As documented in a paper that I published in 2013 and and in one by Rebecca Thomas and colleagues in 2014, hollows are rare in Mercury's high reflectance plains. Thus it may be the mineral phase that causes the LRM to be dark that is also related to formation of hollows.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Dear Sir/Madam, I'm an astronomical public outreach officer from Chiang Mai, Thailand. When I see color of caloris basin in an image from MESSENGER spacecraft. I think Caloris basin has higher albedo (i.e, brighter) than surround area. But the Wikipedia page on the "Caloris Basin" states that "Inside the crater walls, the floor of the crater is filled by lava plains, similar to the maria of the Moon." I find this sentence confusing, because the Lunar maria are dark (contrast with bright Caloris Basin). What is the factor that cause difference between Caloris basin & Lunar Maria? Other type in chemical composition/minerals in the case of Caloris Basin? (While minerals of Lunar maria are Plagioclase Feldspar, Pyroxene, Olivine, Ilmenite) - submitted by Pisit Nitiyanant, Other educator, 03-05-2014

Caloris is a large impact basin on Mercury, similar in form to lunar basins. Like the lunar basins, Caloris has been infilled by volcanic smooth plains deposits. On the Moon, the smooth plains are called "maria" and have lower reflectance than the surrounding rugged highlands. The low reflectance of the maria is a result of the higher iron content of the minerals (chiefly pyroxene and ilmenite) that compose these basaltic rocks. On Mercury, smooth plains deposits do not generally have a strong albedo contrast with the surroundings. Some smooth plains, like those within Caloris, have somewhat higher reflectance than Mercury's average surface. Other mercurian smooth plains have lower than average reflectance. Since we do not have samples from Mercury to study in our laboratories, it is not clear what elements or minerals control the reflectance and color of the mercurian rocks. But measurements by MESSENGER are giving us tantalizing clues that the abundance of sulfur-bearing minerals may play an important role.

You can see a beautiful enhanced-color view of Mercury and Caloris here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

My question(s) concerns timing and rate of thrust faulting. I know that some of the rupes cross cut craters. Any idea when in Mercury's history the contraction occurred? Evidence that it is still ongoing? Any other information regarding shortening rate -- the length of time over which contraction/thrusting occurred? Finally, assuming that there would have been earthquakes/seismicity associated with shortening of a brittle crust, right? Any other evidence for actual earthquakes on Mercury? Beth Geiger, science writer. - entered by Q&A admin, 02-16-2014

Thanks to the amazing high resolution images acquired by MESSENGER, some rupes (or lobate scarps/thrust faults) have been observed to transect very fresh and very small-scale impact craters, some only a few kilometers or less in diameter. From the study of fresh craters on the Moon, lunar craters that are ≤3 km (≤1.9 miles) in diameter are estimated to be Copernican in age, or less than 1 billion years old. The rates at which small craters erode and degrade on Mercury are estimated to be higher than those on the Moon due to the higher flux and impact velocities of bombarding meteoroids. Thus, relatively-fresh impact craters of this size on Mercury are expected to be less than 1 billion years old and may be even younger than comparable-scale features on the Moon. Since some lobate scarps transect these relatively young craters, we know that at least some scarps associated with thrust faulting have been active more recently than the formation of these craters, or within the last 1 billion years. However, we also see lobate scarps that are superposed by more degraded craters that are likely more than ~3 billions years old, indicating that those scarps also have not been active within the last several billion years. Thus, while we are not yet able to confidently constrain how long individual thrust fault scarps have been active, it seems that contraction and thrusting occurred generally on Mercury spread out over several billion years. This thrusting and contracting on Mercury would be similar in many ways to an earthquake on the Earth. We have not yet observed evidence of thrust fault activity on Mercury that is still ongoing today. However, recent Earth-based and MESSENGER observations indicate that the outer core of Mercury is still at least partially molten. Thus recent activity could potentially be occurring on some thrust faults as a result of continuing radial contraction as Mercury's core continues to cool and solidify.

--Maria Banks, Center for Earth & Planetary Studies of the Smithsonian National Air & Space Museum
MESSENGER Geology Discipline Group

Sodium is a liquid at Mercury's daytime temperatures. Wouldn't hot liquid Sodium in the presence of concentrated Sulfur be extremely corrosive - or even explosive? Might this explain the hollows we see everywhere? - submitted by Bryce Johnson, Journalist, 02-12-2014

Thanks for your question Bryce. There are a few things to consider as we try to answer it.

You are correct that the melting point (97°C) of sodium is much lower than the maximum temperatures experienced by Mercury's surface (about 425°C). We also know from MESSENGER Gamma Ray Spectrometer results that there is a substantial amount of sodium on Mercury's surface. Recent analyses have shown that up to about 5% of Mercury's soil (by weight) is sodium. However, we do not expect that this sodium is in its elemental form, but rather it is bound in the structures of minerals that make up the rocks. A likely sodium-bearing mineral on Mercury is the plagioclase feldspar albite (NaAlSi3O8), which is commonly found in many igneous rocks. Albite has a melting temperature of about 1100°C and is therefore resistant to melting even on Mercury's hot surface.

You also note that the surface of Mercury contains abundant sulfur. Again, elemental sulfur (with a melting temperature of about 115°C) is unlikely to be found on Mercury's surface. We believe that the sulfur exists in mineral phases called sulfides. Based on findings from the X-Ray and Gamma Ray Spectrometers on MESSENGER, we think that the most abundant sulfide minerals on Mercury's surface are oldhamite (CaS) and niningerite (MgS), but it is possible that others also exist. These might include the very exotic sounding djerfisherite—K6Na(Fe,Cu,Ni)25S26Cl—or what I imagine you are thinking about—sodium sulfide (Na2S). When this compound comes into contact with air and water it creates hydrogen sulfide and its associated rotten-egg odor. Sodium sulfide is an alkaline substance (it causes skin burns), and it can become explosive at temperatures above 920°C. However, this is not a material that is commonly found in rocks. At Mercury's lower surface temperatures and without an atmosphere that contains oxygen or water vapor, even if sodium sulfide were present, it is unlikely to explode to form the curious landforms called hollows. These enigmatic features, however, are indeed thought to be caused by some type of loss of unstable materials from regions of the crust that are strongly heated by the Sun and/or subjected to intense ion bombardment.

Shoshana Weider, Carnegie Institution of Washington
MESSENGER Geochemistry Discipline Group

It is Andrew Brown again from Ashford, Kent, United Kingdom. I understand that comet 2P/Encke made the closest approach to Mercury today and C/2012 S1 ISON will tomorrow. How did the 2P/Encke observations go and when will we see the best images of both comets? Will both the MDIS NAC and WAC be used? I assume the search for mercurian moons and Vulcanoid asteroids have both reached dead ends with nothing being found? Also would like to say, I think MESSENGER has operated beautifully, Mercury is a fascinating little world and we still have over a year of operations left.

Have the findings from MESSENGER changed the geological calendar of Mercury from the Mariner 10 model?
4,500 million years ago to 3,900 mya Pre Tolstojan.
3,900 - 3,800 mya Tolstojan.
3,600 - 3,700 mya Calorian.
3,700 - 3,000 mya Late Calorian.
3,000 mya to present: Mansurian/Kuiperian.
I suspect that timeline is now too simplistic with evidence of more recent active vents etc? - submitted by Andrew R Brown, Interested public, 11-18-2013

Some images from MESSENGER's observations of comets Encke and ISON were released on Nov. 25, 2013.

With regard to Mercury's geological history, it is important to keep in mind the difference between the relative timescale and the absolute timescale. The relative timescale is defined by stratigraphy and superposition relationships, that is, what units overlie other units. For example, materials deposited by rayed craters like Kuiper overlie (superpose) units of craters with fresh morphology that lack rays (like Mansur). Therefore Kuiperian craters are younger than Mansurian craters. But connecting the stratigraphic (relative) age to an absolute timescale is another matter entirely. In the absence of samples collected from the various units that can be dated by radiometric techniques in the laboratory, we must use indirect means. The chief method is analysis of crater size-frequency distribution. Basically, older surfaces have accumulated more impacts by asteroids and comets than have younger surfaces. On the Moon, scientists have linked the crater counts to the radiometric ages of returned samples. With some assumptions and adjustments involving the difference in the flux of impacting bodies hitting the Moon vs. those hitting Mercury, the crater counts on Mercury can be used to assign absolute ages. Some members of the MESSENGER team are working to revise the ages using data returned by the mission. Some preliminary work is presented here and here.

--Dave Blewett, Johns Hopkins University Applied Physics Lab
MESSENGER Participating Scientist

EW1024960452G_3band_mapped, I noticed some rather intriuging structures to the east about in line with the midpoint of the two large craters, almost look like highly smoothed and reflective domes/fills. Any notions on these? - submitted by Nigel Lavery, Interested public, 11-13-2013

You refer to the Nov. 13, 2013 gallery image, "Burning Inside." This is an an area with a complicated history, where low-reflectance material, pyroclastic deposits, flood volcanism (smooth plains), impact melt, hollows, and chains of secondary craters have all contributed to the rich color and morphological variations in the scene. We examined a monochrome image with different lighting conditions that allow for better perception of topographic differences through shading and shadowing. It does look like there are a few small positive relief features present. These could be domes or knobs of ejecta from the Caloris basin. One such knob is visible at the right edge of the Gallery image from April 5, 2013.

--Rachel Klima and David Blewett, Johns Hopkins University Applied Physics Laboratory

I'm a writer at Universe Today and I have a question on Mercury's vents, like the ones featured in a recent MESSENGER release. (See: A Volcanic View of Mercury) Why do volcanoes on Mercury seem to be flat features, rather than mountainous ones like we have on Earth? Is it related to the planet's gravity at all? Or is it the nature of the eruptions themselves or material that they eject? Would be great if you could help clarify. Thanks! Jason Major. - entered by Q&A admin, 09-25-2013

Volcanism on Mercury (and also the Moon) appears to have been dominated by flood lavas, in which huge quantities if highly fluid (low-viscosity) magma erupts and flows widely to cover a large area. In this type of eruption, no large "volcano" edifice is constructed. The lunar maria and many of Mercury's smooth plains deposits were formed in this manner.

On both the Moon and Mercury there are also examples of explosive activity in which eruptions from a vent showered the surroundings with pyroclastic material (volcanic ash). The vents and bright pyroclastic halos seen near Rachmaninoff on Mercury are examples, as well as numerous "dark mantle deposits" on the Moon.

The types of volcanic features that are formed by an eruption are controlled by factors such as the chemical composition of the magma (which in turn determines how stiff or runny the magma/lava is – i.e., high or low viscosity, and also how easy it is for dissolved gases to escape from the magma), the gas content of the magma (a greater content of dissolved gases will tend to drive explosive eruptions), how fast the magma erupts (slower eruption rates may give time for the gas to get out of the magma gently, thus reducing explosive tendencies, whereas gas in magma that rises rapidly from depth will tend to explode like a shaken bottle of soda pop upon reaching the low pressure at the surface), and the length of the eruption.

Large shield volcanoes (like Mauna Loa on Earth, or Olympus Mons on Mars) are formed by relatively fluids lavas, and a source of magma that is fairly stable for a long time, feeding small/moderate quantities of magma that slowly builds a
mountain from relatively long lava flows and small pyroclastic deposits. Volcanoes like Mt. Fuji or Mt. St. Helens are composed of lava with a different composition that is more given to highly explosive activity and short lava flows, hence tending to build up a steeper mountain than the gentle slopes of Mauna Loa.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory, MESSENGER Participating Scientist

what is Curious about the Raditladi basin? - submitted by Joe Molinar, College student, 04-14-2013

Raditladi is a 257-km diameter double-ring impact basin. It was the subject of a presentation by Louise Prockter and colleagues at the 2009 Lunar and Planetary Science Conference. The interior of the basin has been flooded by volcanic smooth plains. Counts of the density of impact craters on the basin's ejecta suggest that it is about 1 billion years old, young by the standard of large basins on Mercury. Raditladi is remarkable for the beautiful occurrences of hollows on its peak ring mountains and floor. Yet another curiosity about this basin is the presence of troughs on the floor, formed in the volcanic plains by extensional forces that pulled the crust apart. Generally, Mercury's tectonic landforms are formed by the opposite kind of force: contraction, which squeezes the crust together to produce faults and scarps (cliffs).

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I have been on here several times before concerning the Volcanic Pit that is to the west of Copland Crater & NE of Rachmaninoff Basin. The release today: Thursday 21st March 2013. I cannot help but think the pit has been active very recently geologically. Below is some text I wrote myself on my FaceBook page & on the SpacePort V5 forums. What do you think? Also can I ask, if there are any developments on the second mission extension? The fact NASA asked you to continue after the first extension officially ran out, makes me very hopeful that you have the second extension, only that it has not been 'rubber stamped'.
A very high resolution image. This image is the most recent & highest resolution of a series of a volcanic vent I personally suspect of either being active or very recently so. Volcanic Pit is to the west of Copland Crater & to the NE of Rachmaninoff Basin. The MESSENGER team accepted my proposal & when ever MESSENGER is well placed, a high resolution image is obtained. This frame is perfect, exactly as I suggested, an area containing a large part of the volcanic pit with an area bordering to the north that appears in lower resolution images to be incredibly smooth & featureless, suggesting to me, pyroclastic fallout from the vent covering the surrounding terrain. This image is astonishingly clear, showing that even at very high resolution, the terrain to the north is still incredibly smooth & the profiles on the volcanic pit floor are also generally extremely smooth. The area on the pit floor on the right looks like a solidified lava lake to me. What is obvious is a very light smattering of tiny impact craters over the area. There are only a few & widely scattered, suggesting to me that the last eruption was extremely recent on the geological time scale. I do not know what the cratering rate on Mercury is, this is one of the primary goals of the MESSENGER mission, but assuming is similar to our own Moon, then this pit may have erupted within the last one million years. Incredibly recently indeed. The cratering rate may be higher as Mercury only orbits the Sun on average 30% of the Sun to Earth distance, the Sun being the chief gravity well of the solar system. Noting the huge number of tiny comets found approaching so closely to the Sun as seen by the SDO, SOHO & the two STEREO solar observing spacecraft, the cratering rate on Mercury may be much higher, so that reduces further the time since the last eruption of this vent. The land slides on the pit walls also look very recent. Perhaps recent earthquakes due to movement of magma underground ??? Have I indeed discovered an active volcano on Mercury??????
- submitted by Andrew R Brown., Interested public, 03-21-2013

Andrew, Thanks for your efforts to spread the excitement of MESSENGER's exploration on various web forums. The pyroclastic deposit near Rachmaninoff is indeed a fascinating feature. It is so bright that it was noticed in Earth-based images of Mercury obtained by a group of amateur astronomers led by Ronald Dantowitz. Some craters in the 100-200 meter diameter range look like they may have been blanketed by the smooth pyroclastic material, and there are few smaller fresh-looking craters on the smooth material. This certainly suggests that the explosive volcanic activity occurred relatively recently. Detailed crater counts and geologic mapping will be needed to further constrain the age. You are correct that the flux of impactors at Mercury is greater than at the Moon, so a given crater density on Mercury corresponds to a younger age than would the same density on the Moon. Further, impacts on Mercury are known to produce a greater abundance of secondary craters than on the Moon. Many of the craters seen in the image could be secondaries.
The MESSENGER project gave a presentation about the proposal for a Second Extended Mission to a Senior Review Panel at NASA Headquarters on March 14, 2013. The panel is considering the proposal and the material that was presented. NASA may make a decision some time in April.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hello again, I want to ask if the mission watched any change in surface of Mercury or, by the rate of asteroid impact and the resolution of the observations, is it possible to see changes about this issue. Since the first observations, aspects like faults or rough terrain created by contraction and dilation of Mercury have being changing or are they all ancient? Many Mercury years have passed, so did they produce any change in terrain? Because Mercury is closer to the sun, the ratio of impact asteroids is higher, but the force of impact is higher too? If is it so, it is expected that ring walls were higher and created a more rough terrain or like in some observations, by the impact in a hard surface, craters are present with rifling. Like you said solar wind is eroding the surface, volatize material and leaving a harsh crust. By the way, since the beginning of space orbit insertion the hollows did suffer any change? - submitted by Sergio Silva, Interested public, 03-16-2013

It is certainly possible that a large impact could have occurred on Mercury during the time that MESSENGER has been in orbit. It is less likely, though possible, that motion on Mercury's many faults could have taken place. Hollows are thought to be young features that are probably actively forming today. However, by the standards of erosion on Earth, the hollows are still forming at a slow rate: an estimate of the lower limit of the enlargement of hollows published in the journal Science in 2011 was that hollows grow about 1 cm in 70,000 years.
Mercury certainly experiences a greater rate of impacts than that at the Earth and Moon, and the impacting bodies are traveling much faster (average impact speeds on the Moon are about 25 km/s, but on Mercury may be 40 to as much as 80 km/s). The highest resolution images that MESSENGER has obtained have pixel dimensions of about 10 m/pixel. Thus it would be possible to see a new crater of about 20-30 m diameter. However, only a tiny fraction of the planet has been covered at the highest spatial resolution. The science team has targeted many of the hollows for special high-resolution imaging, specifically to look for changes.

--Dave Blewett
Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Regarding the "Fireworks" composite posted 12/31/2012: Have you tried interpolating the sparse spectral data to fill areas of no coverage? This could be accomplished using collocated co-Kriging with a more complete map of Mercury, such as albedo, which should also be related to surface composition.Regards and happy New Year ... outstanding work! - submitted by Kevin Chesser, 12-31-2012

Several different team members have performed various spatial interpolations of the MASCS data. One of the more common so far is averaging inside spatial bins. I have not tried a kriging method yet, but it seems like a logical thing to do. For the image of the day, we wanted to represent the area of the planet directly observed by the MASCS VIRS instrument. I think an interpolated view is a good idea for a future image.

Noam Izenberg, Johns Hopkins University Applied Physics Laboratory
MASCS Instrument Scientist

How do you detect water on a planet`s surface from orbit ? And how do you calculate how much water there is ? - submitted by Robert Hotter, Interested public, 11-30-2012

MESSENGER's Neutron Spectrometer detected abundant hydrogen on and in Mercury's surface near the poles. Water is a hydrogen-rich compound. Thermal models indicate that water ice is stable in the permanently shadowed craters ("cold traps") near Mercury's poles. The Mercury Laser Altimeter detected bright patches in some of the cold traps, consistent with water ice or frost on the surface. The areas of permanent shadow coincide with areas that have unusual high degrees of radar reflectivity, measured by Earth-based radar. Elsewhere in the Solar System, similar radar signatures are associated with water ice (Mars polar caps, icy satellites of Jupiter). Therefore, there is strong evidence that the hydrogen found by MESSENGER at Mercury's poles is in the form of water ice. The amount of water is estimated by measuring the area that is in permanent shadow and multiplying by an estimate of the minimum depth of the ice needed to produce the observed signal. This gives a minimum estimate of the volume of the ice.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Awesome news regarding the confirmation of water ice on Mercury. As for the 'hydrocarbon' deposits, could this mean nitrogen-bearing compounds (ammoniates?) which are frequently detected on comets? The MESSENGER team is to be congratulated for this development.   - submitted by Bryce Johnson, Journalist, 11-29-2012

MESSENGER did not obtain direct chemical information on the organic materials. They are inferred to be present because certain patches are dark (have low reflectance) at the wavelength of the Mercury Laser Altimeter (MLA). Dark, organic materials are found in comets and certain meteorites. As described in the Nov. 29, 2012 press release, the team suspects that the organics and water were delivered to Mercury by impacting comets and asteroids. This is the same process that is thought to have added our oceans to Earth.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hello. I was looking at this website with a friend and we had a few questions. 1. Will there be another spacecraft to follow Messenger? If so when will this spacecraft be launched? 2. What are some explanations why Mercury's silicates are missing? 3. Why does Mercury have unusual radar refelections at the pole? Are there substances causing this? - submitted by Patrick Sycamore, College student, 11-08-2012

1. NASA presently has no plans for a return to Mercury. However a joint European-Japanese project called BepiColombo will send two spacecraft to Mercury - a planetary orbiter in a low-altitude orbit to study the surface, and a magnetospheric orbiter in an elliptical orbit similar to MESSENGER's, designed to study the magnetic field and exosphere. The mission may launch in 2015.

2. A summary of the leading hypotheses that try to explain Mercury's large iron/rock ratio can be found here. MESSENGER's finding of fairly high abundances of volatile elements (like sulfur and potassium) in Mercury's surface suggest that Mercury did not experience extreme heating during its formation and early evolution. This would seem to rule out the giant-impact hypothesis (stripping off much of the planet's rocky outer mantle) and the idea that the planet's outer portion could have been evaporated by an especially hot phase of the early Sun. Thus, it seems that the favored scenarios for Mercury's formation involve the way that the chemical constituents came together (accreted) in the solar nebula. Read more in this Science Highlight.

3. One of MESSENGER's primary goals is to investigate Mercury's polar regions in an attempt to understand what causes the high radar backscatter. The radar properties of materials within Mercury's permanently shadowed craters are similar to those of the Mars ice caps and icy satellites in the outer solar system. Thus it is plausible that ices of water or other volatile compounds have collected in the permanently shadowed "cold traps" over geologic time periods. MESSENGER is attacking the problem by making repeated observations of the polar regions to better map out areas of permanent shadow, and with measurements of hydrogen abundance using the Neutron Spectrometer. Results on the hydrogen abundance should be published soon in the journal Science.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Regarding the October 19, 2012 Gallery image titled 'A Matter of Perspective', I have two questions: 1) Yes, the picture does give the impression one is in orbit over Mercury. . .Just how high above Mercury's surface was the spacecraft when this particular image was taken? 2) There is a bright area on Mercury's surface near the center of the image that appears to have a larger crater. . .could this actually be a volcanic feature? Thanks!

- submitted by Bryce Johnson, Journalist, 10-22-2012

The spacecraft was at an altitude of 4234.3 km when the image was captured. The bright area is a deposit of high-reflectance smooth plains that filled an impact crater. The impact crater is in an area of darker material, known as the "low reflectance material." The plains filling the crater are volcanic lava flows, but the crater was formed by impact.

--Brett Denevi, Johns Hopkins University Applied Physics Laboratory
MESSENGER MDIS Instrument Team

1. What color is Mercury? Why is it grey?
2. What are the white streaks on the surface of Mercury?
3. Does Mercury have any mountains?
4. Is the surface of Mercury solid enough to stand on?
5. How high could you jump on Mercury?
6. How big are the craters on Mercury in comparison to the Great Red Spot on Jupiter?
7.Could a person visit Mercury and survive? - entered by Q&A admin, 10-19-2012

These are great questions from a 9-year-old future scientist. I encourage her to maintain her curiosity about Mercury, the universe, and everything in it. Keep asking questions!

1. You are right that Mercury has color properties that would appear greyish-brown to the human eye. The color is controlled by the composition of the rocks that form
the planet's surface, and the modification that they suffer as a result of impacts of all sizes (ranging in size from dust motes to tens or hundreds of kilometers). The surface of Mercury is also modified by energetic particles (mostly protons and electrons) from the solar wind.

2. The bright streaks that are prominent over much of Mercury's surface are called "crater rays." They are formed when an asteroid or comet strikes the surface. The tremendous amount of energy that is released in such an impact digs a big hole (crater) in the ground, and also crushes a huge amount of rock under the point of impact. Some of this crushed material is thrown far from the crater then re-impacts the surface, forming the rays. Fine particles of crushed rock are more reflective than large pieces, so the rays look brighter. The space environment (dust impacts and solar-wind particles) causes the rays to darken with time.

3. Mountains on Mercury are formed by large impacts. Impact craters on Mercury larger than about 10 kilometers in diameter (about 6 miles) usually have a mountain peak or ring of peaks in the center. The rims of large craters can also be considered as mountain ranges.

4. Mercury is one of the solid-surface bodies in our Solar System. This group includes Mercury, Venus, Earth, the Moon, Mars and its moons, the asteroids, the moons of the outer planets, and Kuiper Belt objects. The outer planets Jupiter, Saturn, Uranus and Neptune are gas giants. They do not have solid surfaces that a person or robotic lander could stand on.

5. Mercury's surface gravity is about 38% of that on Earth. Coincidentally, Mercury has nearly the same surface gravity as does Mars. The height that you can jump is proportional to the reciprocal of the gravity, so on Mercury or Mars you could jump (1.0/0.38) = 2.6 times higher than you could on Earth.

6. Jupiter's famous Red Spot is a storm that has been going on for at least several hundred years. The Red Spot is roughly 30,000 kilometers across in the East-West direction. Mercury's diameter is about 4880 kilometers, and Earth's diameter is about 12,700 kilometers. So the Great Red Spot is much larger than the whole planet Mercury (and Earth)!

7. A human mission to Mercury is possible, but would be extremely complicated and expensive. For example, just to get there takes a long time (MESSENGER needed six years). The travelers would need to take supplies (food, water, oxygen) for the 6-year journey, and for the 6-year return trip, plus for whatever length of stay on the surface was planned. Carrying so much weight means that very large rockets would be needed (keep in mind that you would need to carry rocket fuel for the return trip, too). The conditions on the surface of Mercury are very harsh, and space suits and habitats would need to be designed to withstand the high daytime temperatures and extremely cold nighttime temperatures. I would love to do geological field work on Mercury, but it will probably be many decades or even centuries before humans visit the surface of the innermost planet.

--David Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Scientists are re-thinking the formation of Mercury (because of the high sulfur content). Perhaps Mercury plunged straight though Venus (making it spin backwards) before the Sun's gravity grabbed it. Does that mean the the Rampson Theory of Solar System Genesis (RSG) is validated? - submitted by Chris Rampson, Interested public, 10-16-2012

An impact between Mercury and Venus would be an extremely high-energy/high-temperature event that would be expected to greatly decrease the abundance of volatile (easily vaporized) elements like sulfur in the surviving objects (should the smaller body survive). Consider that the leading hypothesis for the formation of the Moon involves a giant impact between a Mars-sized protoplanet and the proto-Earth. This explains the Moon's low abundance of volatile elements. The MESSENGER sulfur findings are thus evidence against a high-temperature origin for Mercury.

--David Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

 We had a star meeting on 10/10/12 from one of your education out-reach teacher,Brenda Conway.She gave an excllent program on the Mercury mission.There one part that asked questions about the planet's make-up.We had great time talking about the questions and some of our asnwers.My question to you is: Is it possible for Mercury not to be a planet, but ,the core of a small star companion to our sun? It's surface was striped by our sun leaving just the core.This would explain the heavy density of it.Also, it would explain the high levels of potassium,silicon sulfur,thorium,uranium.The uranium is heavy silver-white element,which, could be the white material near the vents.Also, it would explain why there are no volcano domes and the young age of the craters on the surface.

- submitted by George Clarke, Interested public, 10-13-2012

It's great that you enjoyed one of the MESSENGER public outreach presentations. I can't speculate on the nature of a stripped stellar core. However, there are a number of hypotheses for Mercury's formation that attempt to explain Mercury's high density. As you mention, several of these hypotheses are being re-examined in light of evidence from MESSENGER. This new evidence includes measurements of sulfur and potassium, relatively volatile elements that evaporate at relatively low temperature. It turns out that Mercury has a higher abundance of sulfur and potassium than expected. Such elements are not likely to have survived a high-temperature processes (like being inside a companion star). Uranium is a naturally radioactive element. Thus, its abundance can be measured by the MESSENGER Gamma-Ray Spectrometer (GRS). So far there is no indication of large amounts of uranium on Mercury's surface. While volcanic domes have not been found on Mercury, there is extensive evidence of volcanism on the planet, both explosive and extrusive. Mercury's surface is in fact quite ancient. Analysis of the size-frequency distribution of impact craters suggests that the volcanic plains are about 3.8 billion years old.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

scott mcginnis ‏@DaddyWatti : Can we make any inference about Mercury's accretion from the solar nebula based on the surface composition? - entered by Q&A admin, 08-15-2012

One of the major surprises of MESSENGER's investigation of the innermost planet is evidence for a relatively high abundance of volatiles in the crust. This evidence comes from four sources: two are compositional and two are geological. The MESSENGER X-Ray Spectrometer (XRS) has determined that the surface contains as much as 4% of the volatile element sulfur, and the Gamma-Ray Spectrometer (GRS) has measured abundances of the moderately volatile element potassium that are much higher than many models for Mercury's formation would have predicted. Evidence for high volatile abundance also comes from two types of geologic processes that can be seen to have acted on the planet's surface. One of these is explosive volcanism, which produced deposits of pyroclastic materials that were propelled from central vents. Calculations of the velocities needed to eject fragments the distance from the vent to the edge of the deposit can give an estimate of the amount of gas dissolved in rising magmas; it is the exsolving gas that drives explosive volcanism. The identity of the gaseous species is not known exactly, but for the likely candidates, indications are that the gas content of the magma was fairly high. Finally, a landform called hollows, discovered in MESSENGER high-resolution images, is thought to form via a process involving loss of a volatile-bearing phase that is unstable when exposed to the harsh conditions at Mercury's surface.
This evidence for a relatively high abundance of volatiles in Mercury rules out several of the hypotheses for Mercury's formation that involve high temperatures. (Read more about those hypotheses in this Q &A). It may be that material from a wider range of distances from the Sun was incorporated into Mercury as it was accreting that had previously been suspected. Improving our understanding of Mercury's formation will also teach us about the processes that produce many of the "close-in" planets that are being discovered around other stars.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Steve Schaper ‏@sschaper41  Did Mercury ever have a thicker mantle, crust and atmosphere in proportion to those of Venus, Earth and Mars, that it lost due to its location? - entered by Q&A admin, 08-15-2012

Mercury is unusual in that its dense metallic core is proportionally much larger and its rocky outer layer (mantle plus crust) is much thinner than those of the other terrestrial planets (Venus, Earth, and Mars). A number of models have been developed to explain this, including a giant impact that tore off much of Mercury's rocky outer layers, evaporation of the outer rocky layers by a highly hot and active stage of the early Sun, and formation of Mercury from material that had a higher ratio of iron to rock than did the other planets. The first two hypotheses involve high-temperature events that would be expected to leave Mercury greatly depleted in volatile elements (those that evaporate at relatively low temperatures). However, evidence from MESSENGER indicates that Mercury is richer in volatile elements than was previously thought. This finding would seem to eliminate the high-temperature models for Mercury's formation, or at least suggest that those models need to be modified. The planetary science community is actively grappling with the problem of Mercury's origin and evolution, and MESSENGER is still returning more data to analyze and interpret. So stay tuned!
As far as a thicker atmosphere in the past, Mercury may have had an atmosphere early in its history. However, the combination of weak surface gravity (about the same as that of Mars) and close proximity to the Sun causing high temperatures in the atmosphere would have driven the gas molecules to escape. Today Mercury has only a highly tenuous "surface bounded exosphere".

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Govert Schilling ‏@govertschilling: Are there large underground cave systems on Mercury? - entered by Q&A admin, 08-15-2012

Most large cave systems on Earth are formed by dissolution of carbonate rocks (limestone) by the action of groundwater. The carbonate rocks, made primarily of the mineral calcite (CaCO3), were formed by either the shells of marine organisms (like coral) or through non-biological chemical reactions between water, carbon dioxide (CO2) in the atmosphere, and calcium in rocks. It is thought that the early Earth had a much thicker atmosphere that was dominated by CO2, much as Venus still has today. However, the formation of carbonates removed most of the CO2 from the Earth's atmosphere and sequestered it in the carbonate rocks. Mercury, being a much smaller planet with weaker surface gravity, would not have been able to hold on to any primordial atmosphere, and because of its position close to the Sun, temperatures would have been too high to incorporate water in the proportions we have on Earth. Thus, lacking the water and CO2 ingredients for making carbonate rocks, it is unlikely that carbonate rocks, and hence large cave systems, exist on Mercury.
It is possible that small near-surface caves formed by drained lava tubes exist on Mercury. Such caves have been found on the Moon in very high resolution images returned by the Lunar Reconnaissance Orbiter (LRO) spacecraft. MESSENGER's orbit does not permit images at the very high resolution of the LRO data to be obtained for Mercury.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Backroomalien ‏@Backroomalien : Does Mercury have plate tectonic activity? - entered by Q&A admin, 08-15-2012

Mercury, like the Moon and Mars, is a "one-plate planet", lacking the plate boundaries that are the sites of so much geological action on Earth (subduction, mountain-building, volcanism, and earthquakes). Mercury does have a unique style of tectonism, however. The cooling and contraction of Mercury's interior have produced a global system of thrust faulting as the crust was compressed. We see the evidence for this in the many prominent lobate scarps first discovered in Mariner 10 images and now mapped much more extensively by MESSENGER. There are also examples of extensional (pulling apart) tectonic activity on Mercury, in the troughs (graben) associated with some areas of volcanic plains.
-Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Stuart Forbes ‏@StuartForbes1: I would like to know if Mercury's original crust was made of anorthosite. - entered by Q&A admin, 08-15-2012

Anorthosite is a rock made up mostly of the mineral anorthite, a plagioclase feldspar. This mineral is rich in aluminum and calcium and low in iron. Much of the lunar highland crust is composed of anorthosite. Before MESSENGER, telescopic studies of Mercury indicated that Mercury's surface was also low in iron, perhaps even lower that the lunar highlands. Therefore, anorthosite was considered to be a rock type that could possibly be widespread on Mercury.
The MESSENGER X-Ray Spectrometer and Gamma-Ray Spectrometer, however, have made measurements of the elemental composition of Mercury's surface. The low iron abundance suspected from the telescopic spectra has been confirmed, but calcium and aluminum are too low and magnesium too high for the surface to be a lunar-highland-like anorthite-rich rock type. Thus, we are learning that Mercury's composition and the conditions under which it formed are radically different from those that produced the Moon.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Is there any idea of why Mercury has so many of the 'hollows' we see while the Moon has few, if any? The hollows are seen on and around central peaks of craters; also on lava flows. The Moon has both types of terrain, yet no hollows. Weird. - submitted by Bryce Johnson, Journalist, 07-30-2012

You rightly point out one (among many) of the major differences between the Moon
and Mercury. We are still learning a lot about Mercury's surface composition and geology. But it looks like the hollows form as a result of the loss of volatile elements or compounds (that is, those that are vaporized at relatively low temperatures). MESSENGER's X-Ray Spectrometer and Gamma-Ray Spectrometer have found that the elements sulfur and potassium are more abundant in Mercury's surface than predicted by several of the hypotheses for the planet's formation. Sulfur and potassium are relatively volatile elements. We suggested in the paper describing the discovery of the hollows that volatile minerals, probably containing sulfur, are being vaporized by either the high day-time temperatures or by intense space weathering of Mercury's surface (driven by bombardment by micrometeoroids and/or solar wind ions). As the minerals are lost, the surrounding rocky matrix slowly crumbles, eventually producing depressions that can grow and coalesce into the spectacular landforms that MESSENGER has imaged. Rocks from Earth's Moon are greatly depleted in volatile elements, as a consequence of the Moon's formation in a giant impact (a high-temperature event that would have driven off most volatile material). Thus, the type of volatile loss that produces Mercury's hollows does not occur on the Moon. However, the form of the hollows does resemble that of the "Swiss-cheese" terrain found on the south polar cap of Mars. The Swiss-cheese terrain is though to form by sublimation of carbon dioxide ice. So the basic process by which the hollows and the Swiss-cheese terrain form may be similar, though the materials involved are different.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why don't we see more faults in the Mercury craters? If the orbit around the Sun is so eccentric, the difference in heat in surface do not make a erosion effect in craters? Why we see rounded craters and not "cracked" shaped craters by the decompres and compres of materials? Is not enough the difference in temperature? Sorry if it is a silly question. - submitted by Sergio Silva, Interested public, 06-08-2012

Mercury's surface is certainly subject to extreme day-night temperature variations. Thermal expansion and contraction could cause small-scale cracking (along grain boundaries or other zones of weakeness) of rocks on the surface, and hence lead to slow erosion and crumbling. However, the thermal effects would not be likely to cause large fractures. Faults are very common on the planet, but these are caused by the shrinkage of the planet as the interior cooled and contracted - a separate effect from solar heating.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Asked this 2 years ago. Got very nice return letter back, but was told that you couldn't answer this question at that time. So, now 2 years later, I'll try again, and hope you don't think me a pest. Has MESSENGER proven, or DISproven that angrite meteorites DO or DO NOT come from Mercury? Or is it STILL impossible to know for sure? Like the last time, thank you for reading, and thank you for any answer you might be able to give me. Thank you, also, once again, for exploring what I have always felt is one of the most important and interesting planets in our solor system, and making it possible to let us join in the results of MESSENGER's journey. You give us dreams..

P.S. Could we please have more true colour pictures of the whole planet? Once again people are showing black and white photos of the moon and saying thats what Mercury looks like, and once again I'm sick of it. Need to offer proof of the truth again, but for far too long you have been giving us only small sections of Mercury in true colour, or mostly false colours, or black and white.. again. please let us dream of what's really THERE in the colours of Mercury again. Thank you - submitted by Timothy Thomas, 05-03-2012

Angrites are basaltic meteorites, somewhat similar to the much more common eucrite meteorites, except that the angrites formed under more oxidizing conditions than did the reduced eucrites. (The eucrites probably came from the asteroid Vesta.) Basalts are volcanic rocks that originated as lava flows. Even before MESSENGER, it was considered unlikely that the angrites originated on Mercury because of compositional differences. Angrites contain about 10 to 20% iron oxide (FeO), and laboratory reflectance spectra of angrites show strong absorption bands caused by the ferrous iron in the silicate minerals. Mercury's surface, studied by Earth-based telescopes, showed a distinct lack of this absorption feature. Now MESSENGER's measurements of Mercury's reflectance spectrum are available, and the lack of the iron absorption band has been confirmed. Further, MESSENGER's measurements of the elemental composition of Mercury's surface, using the X-ray and gamma-ray spectrometers, give independent confirmation of the low abundance of iron: less than about 4%. Thus it is very probable that the angrites do not come from Mercury.
You are definitely correct that Mercury is not the Moon, and in fact is very different from the Moon in nearly all major aspects. We appreciate your suggestions concerning the images released in the Gallery. Since the spacecraft is now in orbit, not focused on views of the entire globe of Mercury (like the flyby images). Instead, high-resolution images of small patches of the surface are being systematically collected and returned for mosacking. You can explore the monochrome mosaic using the Public QuickMap tool. More effort and calibration is needed to produce good-looking color mosaics of large areas of the surface, but the team is hard at work on that! We will try to feature more "true color" images in the Gallery.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

There is an abundance of both extensional and compressive faults on Mercury's surface. Is there any evidence for sinuous rilles such as we see on the Moon - the type made from extrusion of fresh lava through older solidified lava? - submitted by Bryce Johnson, Journalist, 04-17-2012

The Moon's sinuous rilles are curving valleys that represent former lava channels or collapsed lava tubes. The Apollo 15 astronauts explored near one spectacular example, Hadley Rille. On Mercury there is abundant evidence for volcanic activity involving the flow of lava; the style is similar to that of the Moon but differs in detail. The mercurian lavas appear to have been emplaced in very high volume flows, and the lava must have had a very low viscosity (that is, been very fluid). Both broad and narrow channels are seen. Debra Hurwitz of Brown University and her colleagues gave a presentation at the 2012 Lunar and Planetary Science Conference describing their analysis of lava channels on Mercury. They conclude that the formation of the channels was dominated by thermal erosion rather than mechanical erosion. In other words, the channels were carved mostly because heat from the flowing lava melted the ground over which it was flowing. Research suggests that lunar sinuous rilles also formed as the result of thermal erosion, so the formation of the features is expected to have been similar for both planetary bodies. So far we have observed only a few features that may have formed from lava erosion on Mercury while there are about 200 observed on the Moon, indicating that there are differences in volcanic processes between the two planetary bodies. Debra's abstract shows additional images of lava channels on Mercury.

-David Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

A recent e-mail from Astronomy Magazine reported that Mercury may have a two-layer mantle. The concept involves an upper layer of silicate rock while the lower layer is believed to be mostly iron-sulfide. It wasn't clear if the iron-sulfide was solid or molten and there was no indication (in the article) of how deep the iron-sulfide layer would be. Since major impacts often expose/excavate materials from deep (several kilometers) in a planet's crust, I am wondering if there are any crater ejecta that have shown higher concentations of iron-bearing minerals compared to surrounding terrain? Some of the volcanic vents that have been discovered appear to have ejecta blankets too, so I'm wondering if they might have higher concentrations of iron also? - submitted by Bryce Johnson, Journalist, 03-30-2012

A paper by David E. Smith and colleagues was recently published in the journal Science ("Gravity Field and Internal Structure of Mercury from MESSENGER", 10.1126/science.1218809). Smith reports that the planet's gravity and density could be explained by the presence of a solid iron sulfide (FeS) layer at the top of the iron core. The thickness could be between several tens of kilometers and as much as 200 km. The FeS layer would lie beneath Mercury's outer silicate mantle and crust, which together are several hundred kilometers thick.

The depth of the proposed FeS layer is much too great to be exposed by typical impact craters or basins. One of the major puzzles of Mercury's geology is that the surface rocks are so low in iron content as measured by the gamma-ray spectrometer. Mercury's reflectance spectrum also lacks an absorption at near-infrared wavelengths caused by iron in silicate minerals (this absorption is common on the Moon and many asteroids). Thus, iron on Mercury has been very efficiently segregated between the rocky (silicate) mantle/crust and the iron/iron sulfide core. This is likely a result of the chemical environment ("reducing conditions") under which the planet formed.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Can MESSENGER's instruments detect the presence of so-called 'Rare-Earth Elements' like those found on the Moon by Apollo astronauts? - submitted by Bryce Johnson, Journalist, 02-24-2012

The cosmic abundance of the elements is determined by nuclear reactions in stars and supernovae, where all the elements (other than hydrogen, helium and a little lithium) were made. Rare Earth Elements (REE) are generally hard to detect because they are much less abundant than rock-forming elements like silicon, aluminum, calcium, magnesium, and iron. That's why they are called "rare"! However, certain geological processes can concentrate REE. For example, many REE are "incompatible" elements, meaning that they do not fit easily into the structure of major minerals because of their size or electronic charge. Therefore, they will tend to concentrate in the last liquid portion of a magma as it cools. On the Moon, a large geochemical province on the Nearside is enriched in potassium (K), REE, and phosphorus ( P). Material from this KREEP terrain was sampled by Apollo. Analysis of REE requires samples to be examined in the laboratory using an electron microprobe or other instruments, and thus the REE cannot usually be detected remotely. However, it turns out that two REE, samarium (Sm) and gadolinium (Gd), have unusual nuclear properties. These two elements have exceptionally large probabilities to absorb thermal neutrons. Therefore, scientists can produce maps of their abundance from orbital neutron spectrometer data by first accounting for neutron absorption by major elements like iron and titanium, which are currently being investigated by the MESSENGER gamma-ray and x-ray spectrometers. This technique has been used with data from the Lunar Prospector neutron spectrometer to make a map of inferred Sm abundances on the Moon. It may be possible to use a similar procedure with data from MESSENGER's neutron spectrometer, however the situation is complicated by our lack of samples from Mercury to guide understanding of the major element composition.

--Dave Blewett, Rachel Klima, and Patrick Peplowski
Johns Hopkins University Applied Physics Laboratory
MESSENGER science team

The Mercury surface does not look like the Moon?   Ciao, Carlo - submitted by Carlo Facchini, 02-01-2012

Check out a response to a previous question along similar lines.

MESSENGER has now been in orbit around Mercury for nearly one Earth year. The data returned by the spacecraft shows that Mercury is radically different from the Moon
in nearly every way that we can measure, including composition, internal structure, surface geology, magnetic field, charged particle environment.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I am Andrew Brown agaain from Ashford, Kent, United Kingdom. Must say, what an excellent first update for 2012. It is fantastic to see the S W Claoris volcanic vent in very high resolution with the NAC. Waited since January 2008 when this volcano was discovered in low & medium resolution images during the first Mercury encounter outbound for this view . I am not disappointed!!!!!! The quality of the image is superb & if I am correct, that looks like a landslide on the south wall & very fresh too. The northern part of the vent appears softer. Wonder what the cause of the landslide was? Perhaps the GRS, NS & MASCS may have obtained some elemental data? The vent still looks a little bit like a nested caldera, but the fact the caption reads a Pyroclastic Vent, seems to rule out a shield nature of this feature? What is also immediately obvious is the general lack of impact craters, even at this astonishing resolution of 28 metres, either inside the vent or on the upper slopes. Hopefully it will be possible to date the feature with some sort of confidence. This particular area does not appear to show lava flow fronts, will be interesting to see some further frames & if a pyroclastic vent, than this feature may not rise very high above the surrounding terrain. Will be fascinating to see a MLA cross section. Also any clues as to why this feature is here & why there are not more around & in Caloris? Is this vent related to Caloris or formed much later on due to a magmatic hotspot?

I know lot's of questions!!!!!

Please keep us informed. Andrew. - submitted by Andrew R Brown, Interested public, 01-03-2012

Andrew - Glad you enjoyed the image ../Explore/Science-Images-Database/image.php?image_id=725 . You make a number of good observations. One thing to keep in mind: that image was obtained with a fairly oblique viewing geometry, so some pixels on steep slopes are a bit stretched. This might be what you are interpreting as a landslide. Also, with regard to elemental data from GRS, and NS, recall that they have very large footprints, much larger than the size of the vent feature. MASCS has a much smaller spot size than do GRS or NS; however Mercury's reflectance spectrum is frustratingly free of strong absorption bands that can tell us about composition. The more regional view here: ../Explore/Science-Images-Database/image.php?image_id=199 suggests that the vent is at the summit of a topographic rise, consisent with being a small shield volcano.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

It's me again, Andrew R Brown in Ashford, Kent, United Kingdom. Fascinating updates at the American Geophysical Union Fall 2011 Meeting in San Francisco last week.The entry about the Candidate Pyroclastic Vent, the shield volcano on the SW Caloris Basin. Any news as to when the full resolution frames in that mosaic will be available? The caldera appears to have some interesting structure & that mosaic still shows the volcano to not be too pitted with more recent tiny impact craters. Hope to see the full images soon. Also likewise with the streamlined 'islands' in the lava channels & Pantheon Fossae.

- submitted by Andrew R Brown, Interested public, 12-15-2011

Dear Andrew, Glad that you liked the recent AGU presentations. Indeed, it is an exciting time to be working on MESSENGER and Mercury science, with new images coming in nearly every day! It's really nice to know that the effort we spend posting images on the web is worth it and allows interested people like you to share in the excitement of the mission. We'll try to get some high-resolution views of all the fascinating features around Caloris up in the near future!

--Nancy Chabot, Johns Hopkins University Applied Physics Laboratory
MESSENGER MDIS Instrument Scientist

The image for November 16 features the 'hot pole' at 180 degrees longitude. It was taken in early May. Is there an image of e he 90-degree longitude with comparable resolution available? It would have been on the terminator when the featured image was taken, but maybe it was viewed later. . Thanks! Bryce Johnson, Rockford, Illinois - submitted by Bryce Johnson, Journalist, 11-18-2011

You can browse the entire global MDIS morphology basemap using Quick Map.

David Blewett, Johns Hopkins Applied Physics Laboratory
MESSENGER Participating Scientist

In April, I asked about the possibility of ice in the polar regions. In your response, you mentioned that Messenger's neutron detector needed a few months before it could possibly assess the polar areas. I understand that more than 60,000 images have been taken. Are we any closer to knowing whether there is or isn't ice at the poles? Thank you! - submitted by Dave Kropp, Other educator, 11-17-2011

The polar ice question is being addressed using a variety of techniques, including studies of polar illumination at the south pole using MDIS image data, temperature studies using MLA topography data, and reflectance data using MLA signal returns from permanently shaded craters. In addition, direct measurements of polar hydrogen are being made using the Neutron Spectrometer (NS). The non-NS measurements are providing results that reveal characteristics of the polar regions; however, since I am not involved in those investigations, I am not in a position to discuss their findings.

In regards to the NS measurements, there are number of things I can say. First, we have been very busy analyzing the data and learning what they are telling us. While the information about Mercury's polar hydrogen is embedded within the data, it is taking time to properly tease out that information. Because, in part, of the elliptical orbit of the MESSENGER spacecraft, we are looking for a relatively small signal (4%) that is indicative of large amounts of water ice. Thus, adequate time is needed to ensure the statistical uncertainties are small enough to detect this signal. In actuality, most of the primary mission data is needed to have low enough statistical uncertainties to see the signal of large water ice deposits (I have a paper titled "Predictions of MESSENGER Neutron Spectrometer measurements for Mercury's north polar region" that discusses in detail these aspects of the measurement. A link to this paper is found on the Publications portion of the MESSENGER web site). Second, the NS is directly attached to the MESSENGER spacecraft, the MESSENGER spacecraft carries out all types of attitude rotations throughout its mission, and the spacecraft is in a highly elliptical orbit. This is unlike any other planetary neutron measurement where previous neutron measurements at the Moon and Mars were made from a boom, and/or on constantly nadir pointing spacecraft, and in circular orbits. These unique aspects of the MESSENGER mission (non-boom mounted, time-dependent pointing, elliptical orbit) necessitate a more complex analysis that needs to account for the transport of neutrons through the spacecraft. This analysis is taking time to understand and carry out properly.

In summary, we are taking excellent neutron data, the instrument is working quite well, and we are actively working to obtain results that address the composition of Mercury's polar deposits.

David Lawrence, Johns Hopkins Applied Physics Laboratory
MESSENGER Participating Scientist

Your home page currently features an image showing some of the recently discovered 'hollows'. The bluish/green coloring of these hollows is probably due to the color filtering of the imaging system. Still, I'm wondering if the hollows are anywhere near that color in reality and what kind of minerals might be responsible for the color. Turquoise or jade comes to mind. . .  - submitted by Bryce Johnson, Journalist, 11-10-2011

A portion of the image to which you refer was featured on the cover of the Sept. 30, 2011 issue of the journal Science. The image is an enhanced color presentation, produced by a mathematical combination of images obtained through eight of the MDIS camera's color filters. This works by putting a different color parameter image in the red, green, and blue channels of a computer display. The color parameter images capture specific aspects of Mercury's spectrum (brightness variation with wavelength of light), but the manner in which they are displayed is arbitrary. In other words, we can make the enhanced image look nearly any way we want. Generally we select red-green-blue combinations that correspond in some way to
the color parameters being shown. For example, in the presentation used in the hollows image, red-to-blue variation represent changess in the slope of Mercury's reflectance spectrum. Steeper spectral slopes are described as "red" and shallower slopes are referred to as "blue". The hollows have a "blue" spectral slope, and so appear bluish-green in the enhanced-color image. Mercury's color variations are very subtle, and to the unaided human eye the surface would appear various shades of grey. But MESSENGER's camera and spectrometer allow us to measure these subtle color characteristics and attempt to relate them to the characteristics of known minerals and rock types.

--David Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

The newly discovered 'hollows' are facinating. The higher resolution images seem to show that most of them are on the tops of hills or other elevations. Is this really the case? Also, I can't get over how bright the areas around the hollows are. Can we tell yet if these are either exposed rock (quartz maybe?) or some kind of deposited material? Thanks! - submitted by Bryce Johnson, Journalist, 10-06-2011

The hollows are really a great surprise. In addition to being found on hilltops and crater walls, many are located on relatively flat portions of the floors of certain craters (like Tyagaraja). The hollows are depressions, and may have formed by collapse induced by loss of volatiles in the surface rocks.

The hollows are certainly bright compared to their surroundings. But remember that overall, Mercury is rather dark. The hollows reflect only about 14% of the light (at 559 nm wavelength) that falls on them. For comparison, powdered quartz reflects about 80% of the light at that wavelength. MESSENGER's observations should help us to determine the mineral or process responsible for making Mercury darker than the Moon.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Dear Sir , Ihave been wondering if Mercury's high gravity= density is possibly due to the fact that it could be a nearly naked core of a possibly larger planet that was unable to form do to the heat and other radiation from the Sun that burned off it's outer lithosphere before it could fully form. Sincerely KJE. - submitted by KEVIN Egan, Interested public, 09-30-2011

This is a great question. As you know, Mercury has the highest uncompressed density of the terrestrial planets, implying a larger iron core relative to its total size than those of Venus, Earth, or Mars. In the 35 years since the Mariner 10 flybys, scientists have been developing various models to account for this fact. Some of these models suggested, as you do, that the outer layers were seared off by an intensely hot phase of the early Sun.
However, that model predicts low abundances of volatile elements on the surface, since volatiles evaporate at relatively low temperature. Therefore such elements wouldn't have survived the high-temperature process hypothesized to have removed much of Mercury's original outer, rocky layers. Recent observations of surprisingly large amounts of sulfur on the surface, as well as a large potassium to thorium ratio (sulfur and potassium are volatiles) indicates that the planet was not subjected to the high temperatures required by this type of model. Instead, it may be that Mercury formed from metal-rich material, similar to some types of chondritic meteorites, which can also account for the large core.

--Patrick Peplowski, Johns Hopkins University Applied Physics Laboratory
MESSENGER Geochemistry Discipline Group

I know this is a very generalized question, but if you could break down the composition of Mercury by the "rock", "ice", atmosphere/exosphere, what would the percentages be? - submitted by Michael Bell, College student, 09-15-2011

The mass of possible polar ice deposits and of the exosphere are vanishingly small compared to the mass of Mercury's rocky crust/mantle and metallic core. I heard one MESSENGER team member say that the entire exosphere could fit in a dump truck.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

It is a genuine pleasure to watch this mission progress so well! I am now wondering if we have a definite limit as to the amount of iron in Mercury's surface material. This has been a matter of some controversy for quite awhile. Thanks! - submitted by Bryce Johnson, Journalist, 09-10-2011

Measurements made by the Gamma Ray Spectrometer and Neutron Spectrometer in Mercury orbit are indicating low abundances of iron in the surface of the planet. The latest results will be described at scientific conferences over the next few months.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

One thing that has struck me is the apparent lack of boulders in the sharpest MDIS NAC images released to far.  At that sort of resolution (12 metres) of Mars or the Moon, boulders are readily apparent in many, though not all areas. The 60 metre resolution images of Main Belt Asteroid 21 Lutetia by the ESA Rosetta revealed boulders as did the Galileo Spacecraft did on Main Belt Asteroid 243 Ida at 25 metre resolution. Just seems odd.

Any clues yet as to the relative ages of the lava plains? Did they form at generally the same time or over a prologned period or in fits & starts?

Any idea when the Pantheon Fossae & Caloris Basin Volcano imagery will be released? - submitted by Andrew R Brown, Interested public, 07-27-2011

Most boulders on the Moon are certainly sub 50-meter diameter. They
tend to be associated with Copernican craters. It may be that there are just too few 10-m
resolution MDIS NAC images that have been posted in the Gallery.
In most areas of the Moon there are no boulders at the >10 m scale. One just tends to notice
those that are imaged and thus they seem common.

The MESSENGER team is pouring over the images, assessing the morphology and performing crater size-frequency counts to gain clues to the age of volcanic surfaces. The presence of abundant secondary craters on Mercury complicates interpretation of the size-frequency data. Nonetheless, it is clear that the smooth plains formed over an extended period and that some surfaces are younger than others. Some of the youngest volcanism took place within the Raditladi basin.

The next release of data to the Planetary Data System will be in September or October of 2011. That release will cover the first six months of data from MESSENGER's orbital mission. A number of images will also be released in association with upcoming conference presentations and journal publications.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Regarding scarps caused by contraction. . .   Is this an 'instantaneous' event that happend all at one time, or did it take place over long periods of time? Could these scarps still be rising? - submitted by Bryce Johnson, Journalist, 07-16-2011

The cooling of the planet's interior and associated contraction take place over long periods of time. The faulting that formed Mercury's lobate scarps was caused by this contraction. The faults may move in fits and starts, or slowly and continuously. This is similar to faults on Earth - the San Andreas sticks in places, then ruptures to produce an earthquake. Other parts of the fault "creep" continually. The MESSENGER team will be looking at the abundance of impact craters on the lobate scarps to get clues to their ages. It is conceivable that some are young or still active.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I am very interested in resources in space, and members of the local chapter of the Mars Society subscribe to my newsletter. I would like to know if the hot surface of Mercury, and the slow but regular day/night cycles have concentrated certain elements. Specifically:

Are there identifiable zinc sulphide deposits on Mercury? If so, are there volcanic intrusions into those deposits? Could your mission detect concentrated veins of gallium sulphide or indium sulphide within the zinc sulphide?

Are there other metals that could have concentrated by Mercury's extreme freeze/thaw cycles? Lead is an obvious candidate; other potentials could be tin, thallium, or bismuth. Since you found significant quantities of sulphur, is there also phosphorus and selenium? Other metals could have been somehow extracted out of igneous minerals to be concentrated as salts: lithium, sodium, potassium, rubidium, and caesium. Are these concentrated in veins or pools?

The metal mercury has the same name as the planet, and is liquid here on the surface of Earth. It's interesting because it freezes solid at temperatures found on Mercury's night side, but vaporizes in the heat of Mercury's day. Is there mobile mercury vapour cross the planet? Does mercury frost form at dusk? Or has mercury metal collected in cold traps at the bottom of craters at the planet's poles? - submitted by Robert Dyck, Interested public, 07-03-2011

Elements like gallium, zinc, tin, etc. have low cosmic abundances. On Earth, concentration of these elements has mostly taken place through hydrothermal processes. It is unlikely that such processes have occurred on Mercury. However, the MESSENGER X-Ray Spectrometer has detected several percent sulfur globally in the surface. This is a surprise, since sulfur is a volatile element (i.e., has a low boiling point) and was predicted to be of low abundance by several models of planetary formations. It is unlikely that MESSENGER would be able to detect trace elements, except in the case of gadolinium and samarium. These two rare-earth elements happen to have huge cross-sections for neutron capture, so it may be possible to use data from the Neutron Spectrometer to map areas with elevated abundances. The LCROSS mission, which sent an impactor into an area of permanent shadow on the Moon, found evidence for the element mercury (Hg). The Hg, like other volatile elements and compounds (e.g. water) may also be cold-trapped in areas of permanent shadow on Mercury.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

From the Al/Si and Mg/Si data it looks like Olivine Tholeiitic Basalt or Basaltic Komatiite. Do you have other elemental data, particularly Ca? - submitted by John Dickey, 07-01-2011

Preliminary analysis of gamma-ray data acquired during the first three months of orbital measurements shows signs of possible detection of calcium on the surface. It is possible that after a year of measurements we will be able to determine the average abundance in the northern hemisphere of the planet. We will not be able to make global measurements due to MESSENGER's highly eccentric orbit, which keeps the spacecraft at high altitudes above the southern hemisphere, too far from the planet to detect the gamma-ray emissions from the surface.

--Patrick Peplowski, Johns Hopkins University Applied Physics Laboratory
MESSENGER Geochemistry Discipline Group

I note the XRS instrument has detected 'substantial' amounts of sulfur on Mercury's surface. 1) Are there any numbers available to indicate concentration levels? 2) Have any specific sulfur-bearing minerals been identified? 3) Given that iron and sulfur bind readily, could this discovery shed light on Mercury's (seemingly low) surface iron content? Thanks again! - submitted by Bryce Johnson, Journalist, 06-20-2011

At the NASA press conference held on June 16, 2011, it was reported that analysis of X-Ray Spectrometer data indicates several percent sulfur in Mercury's surface. We have not yet identified the chemical form of the sulfur, that is, what sulfur-bearing mineral(s) may be present. Iron can indeed pair with sulfur to form the mineral troilite (FeS), which is found in some iron meteorites. Iron in troilite would not produce the diagnostic absorption band near a wavelength of 1000 nm that is seen in the reflectance spectrum of the Moon and some asteroids. (That absorption is caused by ferrous iron in silicate minerals like pyroxene or olivine.) Mercury's lack of this absorption band has been a persistent mystery. Data from the MESSENGER Neutron Spectrometer suggests that there is some iron in Mercury's surface, so the trick is to figure out what mineral is hiding it. We hope to do so by synthesizing data from MESSENGER's elemental sensors (XRS, GRS, NS) and spectral information from the multispectral imager (MDIS) and spectrometer (MASCS).

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

This image caption makes the interesting statement that events have "converted much of the soil to a glassy state". Is this wording deliberately avoiding saying "converted much of the soil to glass"? Or is there some interesting non-terrestrial "glass soil" here? (The knowledgebase isn't clear on this.) Regardless of how glassy the soil is, would we expect to see "smashed glass" from space?  Sincerely, K. Richardson

  - submitted by K. Richardson, 05-25-2011

If molten rock is able to cool slowly enough, the atoms and ions in the melt are able to arrange themselves into the most thermodynamically stable configurations, that is, orderly crystal structures. Thus intrusive bodies formed from magma that cooled at depth below the surface and the interiors of surface lava flows that were sufficiently insulated will be composed of mineral crystals that have specific elemental compositions and atomic spacings. However if a melt cools too quickly, the atoms and ions don't have a chance to arrange themselves the way they would like, and a disordered structure results, having no regular atomic pattern. Geologists refer to these materials as "glasses". The rapidly cooled outer skin of a lava flow and a small splash of impact melt are common planetary geological examples of glasses. Micrometeoroid impacts produce tiny bits of impact melt that cool quickly into glasses that coat other soil grains, binding them together into aggregate particles called "agglutinates". The discovery of agglutinates in returned Apollo and Luna soil samples was a surprise; no one had expected them. The rate and flux of micrometeoroid bombardment on Mercury is much higher than at the Moon, so it is possible that Mercury soils that have been developed on the surface for a long time have been converted almost totally to glass.

A glass absorbs and reflects light in a slightly different fashion than a mineral of the same composition. So in some cases it is possible to infer the presence of a glass component in a regolith from the characteristics of the reflectance spectrum.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

A) With all that incoming solar radiation (as I understand it, 13 times the intensity at Earth above the atmosphere and much more relative to what reaches the ground) and those long hot days, would you expect, or be able to detect partial melting or sintering of surface materials? Personally I'm surprised the surface is so fresh-looking, and doesn't have a melted wax appearance to it.

B) With the surface so much warmer than on Earth, it's surprising there isn't more evidence of tectonic activity and volcanism. Do you have any feel as to how Mercury came to be so devoid of radioactive elements it lacks the internal- heat-driven features seen on the much cooler Earth, even after having had billions of years to heat up?

C) Is there any evidence for differences in crater morphology as a function of impactor chemistry? I would think you could tell the difference between a hole made by a snowball and one made by a chunk of solid nickel-iron, but I've never heard this mentioned relative to craters on the Moon or other bodies.      Wonderful site -- keep those pictures flowing! - submitted by Martin, Interested public, 05-21-2011

A) Maximum temperatures on Mercury can reach about 430° C (about 800 °F). Silicate rocks have higher melting points. For example, basaltic lavas erupt at temperatures over 950° C (1470 °F). Granitic magmas form at lower temperatures (about 700° C or 1300 °F), but rocks of granitic composition are not expected on Mercury. Ultramafic magmas have temperatures up to 1600° C (2900° F).

B) There is abundant evidence for tectonism on Mercury. The planet is covered by giant fault scarps (see Beagle Rupes and many other Gallery entries). However, the tectonic activity on Mercury is mainly caused by global contraction, much different than the plate tectonics found on Earth.

Mercury has also experienced extensive volcanism, both explosive and extrusive (lava flows). MESSENGER's Gamma-Ray Spectrometer is making measurements of naturally occurring radioactive elements (potassium, uranium, thorium) that will allow us to compare Mercury's crustal complement of heat-generating elements to the Earth, Moon, and meteorite parent bodies.

C) To first order, the size and form of a hypervelocity impact crater depend on the kinetic energy (mass times velocity) of the impactor. So it can be hard to tell the difference between a crater made by a dense object traveling more slowly and one made by a lower-density object moving at a higher speed, though some subtle differences are predicted by theory and seen in laboratory impact cratering experiments.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Guess what it's me again, from Ashford, Kent, United Kingdom, for a third time!!!!!

Firstly can I say, what a FANTASTIC mission this is, MESSENGER is fulfilling the objectives for those who have advocated for a decent orbital around Mercury. MESSENGER is more than achieving that. Absolutely love this mission & enjoying each & every daily update.

I see that MESSENGER has passed over the Caloris Basin in the early post dawn mercurian morning. Was Pantheon Fossae imaged at high resolution??? You can guess what I am going to ask next!!!! Was the shield volcano in the SW Caloris Basin, seen during the first pass in January 2008, imaged at full resolution with MDIS NAC?? Particularly the 25 KM wide heart shaped caldera & perhaps portions of the flanks???? If so, when will those be released? Another interesting feature Geddes Crater & the unnamed bright pyroclastic vent, seen during the thrd pass in September 2009?

Please keep up the excellent work & very pleased to learn from an update earlier this month that MESSENGER is performing perfectly. This is a wonderful mission, not nearly getting the attention that is deserving. Will also be interesting to compare MESSENGER imagery with those from Dawn of asteroid 4 Vesta soon, which like Mercury has a largely basaltic crust & both are highly differentiated.

Andrew Brown. - submitted by Andrew R Brown, Interested public, 05-19-2011

All the interesting features that you mention have been targeted for high-resolution monochrome, color, and MASCS observations. Of course, the optimum lighting conditions for monochrome morphology images (low Sun) are different from the conditions needed for color and MASCS (high Sun). The images of Pantheon Fossae and Apollodorus crater are fantastic and should help us determine whether the impact triggered the formation of the Fossae, or just formed on top of it. And the dedicated MESSENGER targeting team is about to enter another round of special observations to be ingested into the "SciBox" tool that is used to schedule all of the spacecraft's science observations. Various targeted images will be released in the Gallery after results have been reported at scientific conferences or published in journals.

Several of us on the MESSENGER team are also involved with Dawn, so it will be an exciting summer. One minor correction - although both Mercury and Vesta are differentiated objects that experienced volcanism, we are yet not sure if the lava flows on Mercury would be classified as basalts. We (probably) have samples of Vesta - the eucrite/howardite/diogenite meteorites, which are basalts and pyroxenites.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Sorry, I know the composition is different, but the surface of Mercury looks identical to our Moon. I guess stripped of an atmosphere, all terrestrial bodies would look the same. - submitted by Ray Wallace, 05-03-2011

You are right that the lack of a thick atmosphere leaves terrestrial bodies to a fate of impact battering. However, with MESSENGER in orbit we are starting to see features in high-resolution images that are unlike anything on the Moon. Even from Mariner 10 it was clear that Mercury's smooth plains are not dark, whereas the Moon's smooth volcanic mare plains are dark. Mariner 10 also revealed Mercury's astounding, distinctly non-lunar, abundance of lobate scarps, formed by global contraction. MESSENGER is showing us that there are many more lobate scarps than we expected. Many other strange and wonderful aspects of Mercury will be discussed at scientific meetings and in journal publications for years to come.

By the way, exploration of the Moon in the past five years or so by NASA's LCROSS, NASA's Lunar Reconnaissance Orbiter, Japan's Kaguaya, India's Chandrayaan-1, and China's Chang'E-1 and Chang'E-2 has caused a revolution in our understanding of the Moon and posed many new questions. New rock types that aren't in the Apollo or Luna sample collections have been found by reflectance spectroscopy. Holes have been discovered that allow a peak inside buried lava tubes. Water and other compounds have been found in a shadowed crater. Impact melts that flowed like lava have been mapped at young lunar craters.

So, in short, Mercury doesn't look like the Moon. And the Moon doesn't look like your father's Moon!

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I have a question about something in this image. In the upper quadrant, just below the most pronounced crater, starting from frame in about the 11:00 position there are two distinct bright - for lack of a better term - scarps which extend down then to the right to connect with the large "ghost crater." From the angle of the lighting these do look like genuine escarpments that might be 3-5km in height which means that the entire area in the upper corner of the image may be actually uplifted from the rest of the field. That
area "below" or towards the lower left-hand side of these features appears less heavily cratered. Might this area in fact be some sort of subsidence area, like a freshly created valley where lava might have recently run through obliterating the surface features?
Overall, some really nice initial photos posted to the site.      Thanks.   Bill Havrilla - entered by Q&A admin, 04-22-2011

You have made two good observations. The bright features are indeed lobate scarps, long curving cliff faces that are the surface expression of thrust faults that formed as Mercury's surface buckled in response to cooling and contraction of the interior. Topographic measurements indicate that scarps on Mercury can be up to several kilometers high. Search the Gallery for more images of lobate scarps.

The smoother, less heavily cratered areas to the southwest of the scarps are plains that probably formed by flood volcanism. The thick lavas obliterated many impact craters, forming a new surface that is younger than the geological unit to the northeast. The lavas may have lapped up against the base of the scarps. The younger surface has accumulated fewer impact craters. The size-frequency distribution of impact craters is an important tool that planetary scientists use to determine relative ages on planetary surfaces.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

In 1991, radar studies of a polar region indicated the possibility of ice/snow. Have you proven/disproven this idea yet (for both poles)? If not, when will it be addressed? This is one of the mission's objectives. Thank you for your time.  Dave Kropp - entered by Q&A admin, 04-21-2011

The floors of some craters near Mercury's poles never receive sunlight, since the Sun never rises above the horizon. These locations are thought to be cold enough that water ice could be stable over long periods of time. Earth-based radar studies show that certain polar craters have unusual, high radar reflectivity, a characteristic consistent with the presence of water ice. Another suggestion is that sulfur deposits could be causing the high radar returns. MESSENGER will use it's neutron spectrometer to determine if excess amounts of hydrogen are present over the poles (silicate rocks do not contain hydrogen, but water does). The neutron detector needs time to build up good statistics for detection of hydrogen, but some preliminary indications about hydrogen should be apparent with a few months of operation. The MASCS ultraviolet spectrometer and EPPS plasma spectrometer will also be on the lookout for signs of OH or sulfur over the poles. Topographic profiles by the laser altimeter will reveal whether the shapes of permanently shadowed and radar-bright craters differ from ordinary craters. Ground ice in a crater might cause "terrain softening" and alter its depth or roughness.
Read more about this topic here and here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

 Judging by the new recent pictures that MESSENGER sent back, it's possible that the surface of Mercury is not of uniform thickness or temperature. I am looking forward to seeing reports of how and what the surface is made up of. The impact could have caused the volcano by cracking the surface and allowing the lava to flow out into the crater giving the picture we see today. I wonder if Mercury is growing in size due to volcanic activity.? Or is the planet reclaiming itself? --Sabretip in Canada. - entered by Q&A admin, 04-21-2011

Determining the thickness and composition of of Mercury's crust are major goals of the mission. It is thought that large impact craters cause fracturing of the crust that may allow melts from the interior to access the surface, giving rise to volcanic eruptions. The presence of contractional deformation of the surface shows that Mercury shrank slightly as the interior cooled.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How was there volcanoes in Mercury if there is no atmosphere or water for living things? - submitted by LeeAnna, Elementary school student, 04-12-2011

Volcanism is a geological process that has taken place on all the larger rocky bodies of the Solar System (including Mercury, Venus, Earth, the Moon, Mars, the asteroid Vesta, Jupiter's moon Io). A type of volcanism called "cryovolcanism" has modified the surfaces of icy bodies in the outer Solar System, where the erupted materials are volatile compounds like water, methane, or ammonia. Volcanism happens when internal heat (generated by natural radioactivity, accretional energy, or tidal flexing) causes rocks to partially melt. If the melt is less dense than the surrounding solid rock, the magma can rise to the surface and emerge as an effusive lava flow, or explosively as a pyroclastic eruption. Thus, volcanism is not related to the habitability of a planetary body, or to whether life evolved on that body.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hello again, Thank you so very much for your answers to my previous questions. I really love this mission & am really enjoying what has been released so far. MESSENGER appears to be in superb shape & barring anything unforseen, I think the primary mission will be a breeze along with a vastly extended mission too. I have some more questions / points.

A). When will we see the first NAC images taken from near periherm? I understand these will have a resolution of approx 14 - 18 metres!

B). Has the altimeter been activiated yet during the commissioning phase? If so, what did it tell about the elevation of the terrain passed over?

C). I understand the MDIS commissioning phase concentrated on the Hokusai Crater & surrounding terrain? It would be wonderful to see more of both NAC & WAC of this poorly known area. I like the lava plain image EW0209982350G, overlapping lava flows & mostly small craters. Is there a NAC counterpart?

D). This image of a lava plain & a lava flooded ghost crater: EW0209895977G. Is there a full sized 1,024 x 1,024 version & a NAC counterpart & likewise for this superb image EW0209895911G?

E). Will MESSENGER still carry out occassional Vulcanoid searches & astronomical observtaions from hermocentric orbit? Venus, Earth with Moon & Jupiter at oppositions may be worth obtaining!!!!!!!

Just love what has been released thus far. Like the view of the previously unseen terrain near the south pole & the Debussy Crater images are just absolutely stunning. MESSENGER is already producing great science, despite this being a 'commissioning' phase. :) I am 100% sure, that I will be back.  Andrew R Brown. - submitted by Andrew R Brown, Interested public, 04-03-2011

Andrew: For you, answers now cost 99 p each (Paypal accepted).

A. The highest resolution NAC image collected during the commissioning phase was from an altitude of 550 km, and was binned to a resolution of about 28 m/pixel before being transmitted to Earth.

B. Yes. During commissioning, 14 Mercury Laser Altimeter tracks were obtained, a 7-times increase over the number of profiles recorded during the flybys! We are correlating the topography with features seen in images. Now in the science phase of the mission, two tracks are collected per Earth day. See this daily image release.

C. This is the part of the planet that happened to be beneath MESSENGER's orbit and in daylight at the time the spacecraft arrived. The geology group is debating whether the features in the image you refer to are lava flow fronts or tectonic scarps produced by crustal contraction.

D. You are asking about this image and that one. Both of these WAC images were binned to 512 x 512 on the spacecraft.

E. For MESSENGER's primary one-year science mission, the schedule is filled with acquiring global images of Mercury's surface. Other imaging campaigns are currently a much lower priority and are discussed mainly as potential options for an extended mission. 

A to D: David Blewett, MESSENGER Participating Scientist    E: Nancy Chabot, MESSENGER MDIS Instrument Scientist

Johns Hopkins University Applied Physics Laboratory

Can confirm and adjust the mineral composition of some meteorites that fell to Earth , the chemical composition of Mercury ? - submitted by Tomek, Interested public, 03-31-2011

Most meteorites come from asteroids, and a few originated on the Moon or Mars. Dynamical calculations indicate that it is much more difficult for a piece of material blasted off of Mercury by an impact to enter an orbit that could cross the orbit of the Earth. Thus the chances of one of those pieces falling to the ground as a meteorite are very small. A few years ago, there was a suggestion that the angrite class of meteorites could come from Mercury, but that idea has not gained much acceptance. After MESSENGER completes its compositional survey of the planet, we will have a much better idea of the kind of rocks that could have originated on Mercury. Then the meteorite collections can be re-examined to see if there are any candidate chips off Mercury already in our possession.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

From what I understand, despite Mercury having an iron-dominated composition, it seems there is very little iron in the planet's spectrum. I would have figured the surface should be iron rich with the excavation of lighter atoms from the sputtering that forms to the exopshere. Is the crust truly iron poor? How well can MESSENGER detect and characterise the iron abundance on the surface? What investigations might MESSENGER do to resolve this? - submitted by Thomas Tarrants, Interested public, 03-31-2011

Spectral reflectance measurements made with Earth-based telescopes and by MESSENGER indicate that Mercury's surface lacks ferrous iron in the silicate rocks. However, Neutron Spectrometer measurements made during MESSENGER's three flybys suggest that Mercury's surface has about the same amount of neutron absorbing elements (chiefly iron and titanium) as some mare basalt rocks on the Moon. Thus, it could be that the iron or titanium in Mercury's surface is hiding in a mineral (compound) that does not produce the characteristic ferrous iron absorption. A candidate is iron/titanium oxide minerals, like ilmenite or geikeilite. These minerals have low reflectance, and could be a component of some of the dark regions seen by MESSENGER.

In orbit, the Neutron Spectrometer, Gamma-Ray Spectrometer and X-Ray Spectrometer will all have the opportunity to build up their signals and make much better determinations of the iron abundance of the surface. In addition, the multispectral camera (MDIS-WAC) and spectrometer (MASCS) will make extensive reflectance measurements that may reveal more about the mineralogy of the surface.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I'd love for someone to run statistics on the seemingly huge numbers of double-craters (craters of almost equal size) right next to each other, compared to other bodies. My thought is that during planetary formation, there were plenty of planetestimals "clumped" into doublets (dumbbell-shaped asteroids that hit with low velocities and stuck together in the proto-planetary nebula) in the Mercury growth zone, and they ran into Mercury almost simultaneously. - submitted by Steve Cooperman, K-12 teacher, 03-31-2011

MESSENGER team members are compiling a catalog of all Mercury craters larger than about 20 kilometers in diameter. As the orbital mission proceeds, this database will be filled out with topographic measurements from the Mercury Laser Altimeter and stereo images. Using the locations, sizes, depths, etc., it will be possible to get statistics on the number of similar-sized craters that are close together. The findings could then be compared with similar data for the Moon to determine if there is truly a tendency for Mercury to have more double impacts.

Assuming the picture you released of the giant crater on Mercury is orientated with north at the top what is the structure west of the crater which seems tall enough to cast two shadows ? Thanks John Clark, Colorado - entered by Q&A admin, 03-30-2011

You are referring to the first image obtained from orbit.

(The initial images from orbit have not yet been map projected, but are presented with north generally toward the top. The situation gets more complicated for images of the poles: an image with the North Pole at the center will have south to the top, bottom, left, and right!)

The large crater is Debussy, and the feature to the west is Matabei, which was also seen during MESSENGER's second Mercury flyby.

Matabei is an impact crater that has excavated and deposited dark material from beneath the surface. The dark streaks seen in the image extending southwards from the crater are deposits of material (called "rays") thrown out of the crater by the impact. Most young craters have bright rays (because freshly crushed rock has a higher reflectance than older soils that have been long exposed to the darkening action of the solar wind and micrometeoroid bombardment). However a few craters, like Matabei, dug out inherently dark material - producing dark rays. A few dark-rayed craters are also known on Earth's Moon.

In other words, it is dark material on the ground, not a shadow! (Look carefully at the orientation of shadows inside craters in the image, and compare to the direction of Matabei's rays.)

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I am curious to know if the 'gold ring' in NASA released photo - 531284main_Telecon20110330_466.jpg   is actually gold?

Do you think that much would pay the U.S National Debt? :)   Mark L. Ferguson - entered by Q&A admin, 03-30-2011

The crater you are referring to is named Calvino. It is very interesting because it exposes material of differing composition from the surrounding plains, telling us about the layering of Mercury's crust at this location. Calvino figures prominently in a 2009 Science paper by Brett Denevi and colleagues, and in an Icarus paper published by Carolyn Ernst and colleagues in 2010 (you can see the references for these paper on the MESSENGER publications page).

Of course, the crater rim only looks golden in the false-color composite image. A set of 11 images obtained through different color filters (violet to near-infrared) was processed to emphasize the subtle color differences of Mercury's surface. To the unaided eye, Mercury's silicate surface would appear greyish-brown.

If we do detect a large deposit of actual gold on Mercury (or even a large deposit of mercury on Mercury), the project will immediately alert the public. Enough investors might be found to finance a mining expedition. However, care would be needed to avoid crashing the market by bringing back too much gold at once.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I've just looked at the first photo released to the public. My question is, why are there dark lines at the Matabei Crater? - submitted by Jim Culbert, Interested public, 03-30-2011

You are referring to the first image obtained from orbit.

(The initial images from orbit have not yet been map projected, but are presented with north generally toward the top. The situation gets more complicated for images of the poles: an image with the North Pole at the center will have south to the top, bottom, left, and right!)

The large crater is Debussy, and the feature to the west is Matabei, which was also seen during MESSENGER's second Mercury flyby.

Matabei is an impact crater that has excavated and deposited dark material from beneath the surface. The dark streaks seen in the image extending southwards from the crater are deposits of material (called "rays") thrown out of the crater by the impact. Most young craters have bright rays (because freshly crushed rock has a higher reflectance than older soils that have been long exposed to the darkening action of the solar wind and micrometeoroid bombardment). However a few craters, like Matabei, dug out inherently dark material - producing dark rays. A few dark-rayed craters are also known on Earth's Moon.

In other words, it is dark material on the ground, not a shadow! (Look carefully at the orientation of shadows inside craters in the image, and compare to the direction of Matabei's rays.)

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Although it is currently assumed that the volcanoes on Mercury are extinct, is it possible that they are still outgassing? Also, given the intense heat and radiation that Mercury receives being so close to the Sun, are the soils on Mercury still outgassing to contribute to Mercury's exosphere? How has Mercury's soil been altered by the Sun's radiation? - submitted by Ralph Ricketson, Interested public, 03-25-2011

It is certainly possible that Mercury today has some minor activity such as escape of gases from the interior. The Lunar Prospector spacecraft detected releases of radon gas from a few locations on the Moon; the radon comes from the decay of naturally occurring uranium-238. Such releases are likely to also take place on Mercury. In addition to gas produced by radioactive decay, other volatiles may be escaping from Mercury's interior. The explosive volcanic eruptions that produced the pyroclastic deposits seen by MESSENGER were driven by dissolved gases as they escaped from the rising magma. The identities of the gases are not known, but plausible candidates include CO, CO2, H2O, SO2, and H2S. Work done by Laura Kerber and James Head of Brown University in 2009 suggests that the volatile content of the magmas was several thousand parts per million (see the MESSENGER publications page). Gases like these could continue to leak out over the history of the planet.

Mercury's regolith is not "outgassing" in the same way, but the surface is in fact the source of the heavier elements in the exosphere.

Soils on an airless planetary body experience alteration by several processes, collectively called "space weathering" by planetary scientists. Much of our knowledge of space weathering comes from study of samples returned from the Moon by Apollo astronauts and Luna robots. Micrometeoroid impacts break up surface materials. Melting and vaporization are caused by both micrometeoroid impacts and by "sputtering" by energetic ions from the solar wind or magnetosphere. The melts cool rapidly, creating splashes of silicate glass that weld together rock and mineral fragments. These glass-welded composite particles are known as agglutinates. Vapors condense and are deposited on surrounding soil grains, producing glassy rims. Chemical reduction takes place in the vapors, causing ferrous iron in silicates to be converted to tiny (sub-micrometer in size) blebs of metallic iron. On the Moon, the submicroscopic iron particles are the cause of the strong optical changes that accompany exposure to the space environment. A lunar soil with a long exposure history is much darker and has a steeper ("redder") spectral slope than the rock from which is was derived. MESSENGER observations during the primary mission will help us to better characterize the style of space weathering on Mercury.

--David Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hello !,have you notice the huge crater rigth in the midle of picture taken on 7 jan 2011? ; i have seen others craters on martinan ground as the mount Olimpus, I am not sure because I am seen on my notebook, may be is so big as the martian volcano !!, from El Salvador,jose - submitted by jose gonzalez, Interested public, 03-25-2011

MESSENGER was not near Mercury on January 7, 2011, so no images of the planet were obtained on that day. During its first Mercury flyby on January 14, 2008, MESSENGER did collect images of a volcanic construct inside the Caloris basin. Olympus Mons on Mars is a gigantic shield volcano (600 km across and 24 km high, with a 90-km diameter summit collapse crater [caldera]), the product of extensive volcanic activity over a long period of time. The Mercury Caloris volcano is much smaller - about 100 km across with a 20-km irregular central depression - and resulted from much more limited explosive and effusive activity than that which took place on Mars.

I was wondering about volatiles and the history of making mercury. The early history of mercury is like baking a chemistry sample dry til its mass stays the same, a dry, moonlike sample.  

1) After the initial dry stage, is there any evidence of later historical additions from the liquid core or evidence explosive volcanism deposits on the surface? 

2) What scenarios are there for this? Could comets have re-added volatiles later on in mercury's history?

3) Are there any differences or similarities between later addtion scenarios between mercury and Earth? Earth had its early bake out period in the initial bombardment. Did mercury's later additions of volatiles fail or why did earth's succeed. Anything testable? - submitted by RobertInOKC, Interested public, 03-24-2011

The core is iron metal, which is much more dense than the silicate mantle. There is no known way that molten core material could get to the surface against gravity after the planet and core formed, short of a catastrophic impact disruption of the entire planet.

We do see evidence for pyroclastic deposits formed by explosive volcanic eruptions. These eruptions were driven by volatile gas that was present in the magma at depth.

Certainly water has been added to all the terrestrial planets throughout the history of the Solar System by the impact of comets and also meteoroids containing hydrated minerals. In fact, all of Earth's ocean water may have been delivered by comet impacts. Mercury's hot surface, lack of atmosphere, and weak gravity make it very hard to hold on to any water that was delivered to the surface. However it is likely that some water migrated to permanently shadowed cold-traps near the poles, and resides there today in the form of ice

--David Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist


Extreme tempeture differences on Mercury: Does the extreme temp differences cause any changes on rock or proportional size of the planet. Warm= expands / cold = contracts. - submitted by Lewis Mccane, Interested public, 03-24-2011

Mercury's surface can experience great temperature swings, over 1000° F, from day to night.There is evidence that temperature affects the way in which some common rock-forming minerals absorb and reflect light. We will be looking for color differences that correlate with temperature to see if this process is happening on Mercury's surface. The extreme temperature cycling and corresponding expansion and contraction might be a process contributing to the break-down of Mercury surface materials, analogous to freeze-thaw frost wedging that can disaggregate rocks (and roads) on Earth.

It is clear that Mercury has shrunken slightly over geological time, causing its surface to crumple. Long curving cliffs ("scarps" in geologist lingo) indicate the presence of faults where one section of the crust had been pushed up over another. These giant scarps are thought to have formed as Mercury cooled and the entire planet contracted on a global scale.


--David Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Hello there, I am Andrew Brown, in Kent, United Kingdom.

Concerning the shield volcano on the south west boundary of the Caloris Basin discovered during the first Mercury pass in January 2008.

1). Given a width at the base of 75 KM / 47 miles & the average shape of shields on Venus, Earth, Mars & Io I make that shield volcano to be a very respectable 3,800 metres / 12,500 feet tall or similar in height to Pico del Teide on the Canary Island of Tenerife. Is there any evidence to support my figure?

2). Once in Hermcentric orbit, will the MDIS NAC get some very high resolution images of the volcano as is not too far from the latitude that MESSENGER will be at periherm (closest point to Mercury)? Perhaps cross sections like the MRO HiRISE strips of Mars or the LRO LROC NAC of the Moon, or perhaps even whole mosaics of the volcano? There may be collapsing lava tubes & / or lava flows visible. Given the number of sumperimposed small impact craters, the volcano to me looks as though it has been extinct for quite some considerable time.

3). The 35 KM / 15 mile wide summit heart shaped nested caldera looks interesting. Will be great to get some high res views of that.

4). Rembrandt Basin: unfortunately MESSENGER will be close to apoherm (furthest point in an orbit around Mercury).I assume the images already of Rembrandt Basin will remain the highest resolution?

5). Assuming all goes well, which by all indications so far they will, MESSENGER will almost certainly last well into an extended mission. If so, could the orbit be 'flipped' so that periherm can occur over the Rembrandt Basin & carry out a similar kind of survey as will be done with Caloris Basin during the Primary Mission?

- submitted by Andrew R Brown, Interested public, 03-16-2011

Wow, Andrew, you are a real planetary geo-nut! We are glad to have serious fans like you.

I've answered your questions 1, 2, 3, and 5; Scott Murchie (MESSENGER Co-Investigator at JHU-APL) tackled #4.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

- - - - - - - - - -

#1) The volcanic feature you refer to can be seen here. During the primary mission, the topography of Mercury's surface will be determined both by the
laser altimeter (MLA) and by way of MDIS stereo images. We will soon be able to test your prediction for the height of the mountain!

#2) This volcanic construct is of high interest to the MESSENGER Science Team. In addition to systematic mapping,
MESSENGER's instruments (including the WAC, NAC, MASCS, and MLA) will be making special
targeted observations of several thousand specific features. The volcano you mention is
among those special targets. The Geology Discipline Group will be on the lookout for just the kind
of features you mention: lava flow fronts, lava channels or collapsed tubes (rilles), small vents, and
so forth. New high-resolution images will permit better crater counts to be performed, giving
a better idea of the volcano's age. Spectral reflectance information from MDIS and MASCS will provide
clues to the composition of the various volcanic deposits.

#3) The caldera (summit crater) will be another subject of special targeted observations. Stay tuned for the findings!

#4) Rembrandt basin is centered at about 33 degrees S, and is 716 km in diameter. It is a bit less than half the diameter of the Caloris basin.

During flyby 2, Rembrandt was imaged from MESSENGER with the spacecraft
inbound to a closest approach point nearly on the other side of Mercury from
Rembrandt. Hence the line-of-sight distance to the basin was over 16000 km,
and the images were no better than 440 meters per pixel. However this number
is a little deceptive because the view to Rembrandt was very oblique, degrading the
effective resolution by about a factor of two in the east-west direction to -
effectively - about 900 meters per pixel.

Once in orbit, Rembrandt can be imaged at nearly ideal lighting at spacecraft
nadir, with the low point in the orbit on the same side of the planet as
Rembrandt. Thus the images will have a line of sight range of only about
7000 km, and will view the surface at a near-normal geometry with
resolution of about 200 meters per pixel or better.


#5) The entire team is looking forward to a successful primary mission (one Earth year in length), and is hoping that
NASA will approve an extended mission. For the extended mission, it would not be possible to change the
orbit so that the closest approach (periapsis, or periherm) is over the southern hemisphere - that would
require far more fuel than the spacecraft has available. However, some far less radical modifications to the orbit are being considered.

Mercury's interior structure, magnetic and gravitational field, and related matters

Hi. From what I have read it seems iron turns from liquid to solid at the core's outer boundary but does the core also have a solid inner core as originally proposed? How much of the core is liquid? Many thanks. - submitted by Pauline Macrae, 04-01-2015

One of the guiding topics for the MESSENGER mission has been the determination of the size and state of Mercury's core. It is indeed true that one of the hypotheses to explain MESSENGER observations of Mercury's gravity field is that there might be a solid portion of the core at its outer boundary. This solid layer might arise from the separation of two immiscible liquids (that is, things that won't mix - similar to oil and water) in the core. The lighter of these liquids would rise to the top of the core and might solidify a layer of iron sulfide. The denser liquid below this layer might also solidify, though more likely as a solid inner core as on the Earth. It is also possible that the layer at the top of the core is not solid, and perhaps only a solid inner core exists. At present we do not have enough information to determine the amount of the core that is liquid with great certainty. Future work analyzing Mercury's gravity field and the operation of its magnetic field, which is generated in the liquid part of the core, should improve our knowledge of how much of the core is liquid at present.

--Steve Hauck, Case Western Reserve University
MESSENGER Participating Scientist

Dear Messenger team,I am writing a novel set on Mercury in the year 2288. Your data has been invaluable! I have one question which does not seem to be answered in the knowledge base, and hope you can help.At the end of the book, my characters are stuck on the dayside of Mercury at latitude 75 North. Based on your animation, I assume that the temperature at any given location would not climb above 100 C until the sun had already been up for an Earth month. If so, it is NOT the case that sunrise itself would frizzle them like sausages. They could survive for at least an Earth month. Their spacesuits have a temperature tolerance of 150 C. So they would not be in danger of melting until the sun had been up for a whole 45 Earth days! Is this correct! Part two of this question: The characters seek shelter in the shade of a scarp. Is it the case that such a shadow would stay cold even when the sun was high (although obviously the shadow would vanish when the sun reached its zenith), and if so, approximately how cold? Thank you for your help, and for your scientific endeavors! - submitted by Curious Author, 12-02-2014

1- At latitude 75 deg. N, the surface temperature would likely climb above 100 C in approximately 10-15 Earth days after sunrise. In terms of local time (remembering the mercurian day is about 180 Earth days), that would correspond to approximately 7:30-8:00 am local time, depending on the longitude under consideration. This in part due to the variations in temperature experienced by different longitudes on the planet. Near Mercury's "hot poles" (0 and 180 longitude), the temperature would be reached earlier, as compared to the "cold poles" (90 and 270 longitude) where the temperature would increase more slowly. Keep in mind that the general temperature calculations are for an ideal smooth, spherical planet: Local slope and topography would also have an effect (increased or reduced incident flux, and/or shadowing). Any ground surface that "sticks up" above the ideal sphere will receive more solar flux per unit area, and hence experience greater heating. This also applies to an astronaut standing up vs. lying down!

2- Sheltering in the shadow of a scarp would certainly afford protection from the Sun's direct rays. The temperature within the shadow would strongly depend on the exact geometry of the surrounding topography. This is because topography can contribute two kinds of indirect heating. First, nearby surfaces that are sunlit will reflect some sunlight into the shadow. Second, surrounding sunlit areas will heat up and radiate substantial infrared (thermal) flux into the shadow. So the best scarp shadow to hide in would be one for which any facing slopes (like crater walls or other scarps) that could contribute to indirect heating are far away.

Erwan Mazarico, NASA Goddard Space Flight Center

Dave Blewett, Johns Hopkins University Applied Physics Laboratory

hi, i have a doubt is there any temperature in spacce, if temperature is there then how much it will be? - submitted by ganesh, College student, 06-01-2014

Temperature is a property of matter. "Space" is a vacuum, and hence does not have a temperature in the conventional sense. A material that is exposed to the vacuum of space - for instance the surface of an airless body (like Mercury, the Moon, or an asteroid), or the structure of a spacecraft - will reach a temperature that is a balance between the sunlight warming the surface and the thermal energy radiated away to space. Thus the dayside surface of Mercury can reach high temperatures (about 800 deg. F), but at night the surface temperature plunges to as low as -300 deg. F.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

MESSENGER has been in orbit for nearly twelve Mercury years. Do we see very noticeable patterns of changes in the magnetic field's behavior over the planet's year? - submitted by Bryce Johnson, Journalist, 01-22-2014

We do! The magnetic field of the planet itself does not appear to change, but its interaction with the solar wind and interplanetary magnetic field does. The solar wind is a magnetized plasma flowing nearly radially outward from the Sun at speeds of 400 to 700 km/s, faster than any wave mode in the solar wind. The mass density and hence the pressure exerted by this flow vary with distance from the Sun, more than doubling from Mercury's aphelion (0.47 AU) to Mercury's perihelion (0.31 AU). As a result, Mercury's magnetopause boundary between the solar wind and the planetary magnetic field moves in and out in concert with the Mercury-Sun distance. The intensity of magnetospheric disturbances, the density of plasma in Mercury's magnetosphere, and other phenomena also wax and wane over the Mercury year. Indeed this regular variability is proving to be a useful tool to probe different aspects of the magnetosphere and even the interior of the planet. Watch for those results to be released this spring and summer!

--Brian Anderson, Johns Hopkins University Applied Physics Laboratory
MESSENGER Deputy Project Scientist

During Messengers continuing trips around Mercury were there any anomalies in the planets gravitational field detected toward the sun during the closest portion of Mercury's oval orbit? I realize the space craft does not have gravity sensing equipment on board but does its flight path bring it directly between the planet and the sun at the close point to be effected by any variations? - submitted by Gary L, Interested public, 07-08-2013

We use Doppler shifts in MESSENGER's radio frequency transmissions to Earth to determine Mercury's gravitation field. This is the same method used to determine the gravity fields of every celestial body that has had a spacecraft flyby or go into orbit. The spacecraft itself is the gravity-sensing instrument. Mercury's gravitational field affects MESSENGER's speed, causing Doppler shifts in the frequency of the radio signal. These small shifts are measured accurately, to better than one part in a trillion.

The Sun also affects MESSENGER's motion, and we must account for this when determining Mercury's gravity. The effects of the Sun's gravity depend on distance to the Sun, so yes, these effects are stronger during Mercury's perihelion. MESSENGER is much farther from the Sun than from Mercury, so the Sun's influence—the effect of its gravitation field—on MESSENGER's velocity is relatively smooth and well known.

Mark Perry, Jopkins University Applied Physics Laboratory
MESSENGER Geophysics Discipline Group

Is Mercury's gravity field "lumpy" like the Moon's? Is the currnet MESSENGER orbit stable in the long term (decades)? - submitted by Chuck Norisez, Interested public, 03-18-2013

No planet is a perfectly homogeneous sphere, so all planets have "lumpy" gravity to some extent: impact craters and basins have dug holes and redistributed material to form ejecta blankets and rim and central peak mountains. Volcanic plains have erupted to fill many low-lying areas with layers of rock that are more dense than the surrounding impact-fractured crust. Intrusions of dense solidified magma may lurk beneath the surface in certain locations. Dense mantle rock may have been uplifted beneath impact basins. These density variations produce varying gravitational tugs on an orbiting spacecraft, making it necessary to occasionally use thrusters to maintain the orbit. However, at Mercury there is another, larger problem that does not affect lunar orbiters: the Sun's gravity. Perturbations by the Sun distort MESSENGER's orbit around Mercury. The result is to lower the periapsis (lowest point in the orbit); if uncorrected, the periapsis altitude will, over a period of months, reach zero and the spacecraft will crash into the surface. If NASA approves a second Extended Mission for MESSENGER, three or four orbital correction maneuvers will be performed during two years to boost the periapsis and allow continued operations.

--Dave Blewett
Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Hi, what is the best estimate of Mercury's mass? I have seen values ranging from 3.30104 x 10^23 kg to 3.285 x 10^23 kg to a whopping 1.99 x 10^30 kg. Do we know the mass of MESSENGER precisely enough to estimate Mercury's mass from its orbit? Thanks! - submitted by Jerry, Interested public, 12-26-2012

A paper by David Smith and colleagues published in 2012 (Science vol. 336, pages 214-217) has the latest result for the planet's mass: GM=22031.780 +/- 0.02 km^3/s^2. In kilograms, this is 3.3012x10^23 kg, close to your first number. We know mass less accurately than GM because G (the gravitational constant) is only known to four decimal places. (The relative uncertainty in G is 1.2x10^-4.)

Actually, we do not need to know MESSENGER's mass very accurately. Since it is so many orders of magnitude lower in mass than Mercury, MESSENGER does not affect Mercury's motion. Accurate measurements of MESSENGER's motion about Mercury provide Mercury's mass. The uncertainty in other forces such as solar pressure are the major contributors to uncertainty in Mercury's mass.

Mark Perry, Johns Hopkins University Applied Physics Laboratory
MESSENGER Geophysics Discipline Group

First i will tell the information that i have, second i will a make an question that could be relevant if the first part is accurate. First part: I know that earth is little flatness in his shape, because of centrifugal forces. The velocity of spin in his axis is the cause of this situation. Other planets rotate in their axis, so i suspect that they are somehow a little flatness too (I don't have in account how different they are in their core: mercury is more massive than earth, who could have implications about what i will tell). So i suppose that in the past, he (mercury), was a little flatness too. Another assumption, when he cooled off and shrank, i think that his flatness increased too because, in first place, is mass was concentrated in his equators. When i see long range pictures of the poles, i see rough features that are very predominant and seems that they partially collapse. About the surface, by what I know, the features that prove the shrinkage of the planet were deliver to faults in his surface. The hollows explain the vanish of possible volatile materials by the action of solar wind. So what’s explanation of this rough, and somehow, strange poles? - submitted by Sergio Silva, Interested public, 11-29-2012

The team is working to determine Mercury's oblateness from MESSENGER data, but that analysis is not yet complete. Rotational flattening is a well known phenomenon on planetary bodies, but it is not clear to what extent a fossil bulge may be present on Mercury.

Images of the polar regions necessarily contain extensive shadows, simply because at high latitudes the Sun is always close to the horizon. This tends to give the polar regions a rougher appearance than areas at equatorial and mid-latitudes that can be photographed with the Sun high overhead, minimizing shadowing. So in fact, the polar regions are not rougher than elsewhere on the planet, and there are no collapse features. There are extensive smooth plains (volcanic lava) deposits near the north pole.

--James Roberts, Mark Perry, and Dave Blewett
Johns Hopkins University Applied Physics Laboratory

What i want to know if in a massive outburst of solar flare could disrupt the gravitational forces of the sun. In other celestial bodies gravity is represented like it was formed by spherical bodies. But when great mass were released, like in June of 2011, didn't this event have consequences in small gravital disruption in other celestial bodies and communications (i don't mean in interferences but small delays or premature signals? Could spherical models be applied to stars in facts like gravity? Am i right? Messenger could study this. - submitted by Sergio Silva, Interested public, 10-01-2012

The mass of material ejected in a solar flare is negigible compared to the mass of the Sun. Thus the Sun's gravitational field continues to be well represented as that of a spherical "point source" as far as the orbits of the planets go, and similarly for relativistic effects due to the Sun's spherical mass.

I am a retired physicist from Universidad de Oriente at Cumana,Venezuela. My present interest is to make some fine relativistic corrections to planets perihelion precession as well as orbital periods . Concerning relativistic periods, how accurate is Messenger to measure the orbital period of Mercury and by how much does it differ from Kepler´s third law estimate ? Best regards, Professor Jose M. Saca. - submitted by Jose M. Saca, 06-02-2012

MESSENGER navigation teams do not to my knowledge routinely solve for the period of Mercury. The JPL DE423 planetary ephemeris is assumed for Earth and Mercury and the appropriate equations of motion for MESSENGER are solved in the solar system barycentric inertial frame, fitting the radio tracking data. As you know, the JPL navigation teams incorporate general relativistic corrections to the dynamical equations.
 The radio tracking system is described in

MESSENGER tracking from the flyby encounters was used to adjust the orbital elements of Mercury in the Development Ephemerides produced by JPL - see
I believe the several Mercury years of MESSENGER orbital data will eventually be included in the DE products.

We would like some day to repeat a two-way laser ranging asynchronous transponder experiment using the Mercury Laser Altimeter as was performed during cruise in 2005.
That experiment verified a relativistic delay in the calculated light time due to Sun's gravity at a distance of 30 million kilometers from Earth.

--Greg Neumann, NASA Goddard Space Flight Center
MESSENGER Geophysics Discipline Group

I would like to know whether MESSENGERcompleted its gravity field search on the interior of Mercury and what the results are thus telling us how the planet is from crust to core. Also I would like to know if any cracks like hollow cavities exist within the planet. This I deduce from the continuous heating and cooling of the planet. - submitted by pantelo pandeli, Journalist, 05-08-2012

 Analysis of Mercury's gravity and interior structure was recently published in two papers
in the journal Science:   and

It is not possible for there to be large voids deep within a planet. This is a simple consequence of the limited strength of rocks, and the tremendous weight of overlying material. In the shallow subsurface there may be features such as fractures or lava tubes. It is possible that stresses caused by expansion and contraction in response to heating and cooling could cause fracturing of rocks on the surface.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

When Mercury gets close to the Sun , does the core  get hot enough to cause volcanic activity. How hot does the surface of Mercury get during the time nearest the Sun? - submitted by John, 10-24-2011

Mercury's orbit is more elliptical than that of the Earth, so the amount of solar heating from its closest to farthest point from the Sun varies significantly. To see an animation of Mercury's orbit and surface temperature, look here.

The Sun's heating of the surface has little or no effect on the temperature of the deep interior of the planet. Below the "thermal skin depth" of a few meters, the temperature does not vary from day to night or from season to season. (Rocks are very poor conductors of heat.)

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Is Mercury still still seismically active? I would love to see a high res, linked combination of surface elevation and feature location, chemical composition, and temperature gradation as it changes over time. - submitted by william plowden, Interested public, 07-14-2011

We won't know for sure until seismometers are landed on the surface of the planet. However, Mercury is covered by numerous and large scarps, which are the expression of thrust faulting. Some of these scarps appear to be lightly cratered, implying that the faults may still be active. The seismometers placed on the Moon by the Apollo astronauts recorded signals from impacts as well as internal quakes. It is likely that flexing of Mercury's crust and mantle as it moves in its highly elliptical orbit would also generate internal seismic events.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Dear Sir. I work in the aerospace field, and I have a physics PhD. There is nothing about my question in your archives. I am wondering if anyone has done a rough calculation of the underground temperature of Mercury vs. depth and latitude? I understand that the equatorial surface temperature changes between 90K and 700K as the planet rotates. But below 1-2 meters, the temperature would be relatively constant somewhere between these two extremes, and it would vary with depth and latitude. I am wondering if there is some depth and latitude where the temperature is a balmy 296K (room temperature)? If so, an underground base could be put there, and the underground location would also provide shielding from ionizing radiation, and it would make the lack of atmosphere less important. In addition, the strong solar radiation on the surface would provide unlimited power via solar arrays. And with unlimited power one can make almost anything needed for survival. Finally, if there is some depth and latitude where the temperature allows a Mercury base, why not a whole Mercury colony in an underground ring circling the planet?

- submitted by Dr. James Shifflett, 06-22-2011

Modeling of Mercury's subsurface temperatures has been carried out for several purposes, including finding the depth at which rocks are below the Curie temperature and hence could retain a magnetic signature, relating temperatures to the mechanical behavior of rocks to help understand tectonic features, and to determine the stability of polar volatile species. Modeling by David Paige of the University of California at Los Angeles indicates that at 84 degrees North, 90 degrees East (i.e., a longitude opposite Mercury's "hot poles"), the mean annual temperature at a depth of 1 meter below the surface is about 120 kelvin, suitable for retaining water ice. Moving toward the equator, the depth to a given temperature will increase.

So certainly there are many locations where an insulating layer of regolith could provide for stable, temperate conditions. Getting humans to Mercury and constructing extensive subterranean habitats would be a challenging and expensive undertaking, however.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Dear Sirs: Now that one Mercury year (one complete orbit) has gone, have you some information about a measurement of Mercury's period ? I will appreciate your reply. Jose M. Saca. - submitted by Jose M. Saca, Other educator, 06-18-2011

This is a great question. The orbital period of Mercury and its distance from the Sun are related by a simple formula to the mass of the Sun, a result that was first established by Johannes Kepler (1571-1630) but not fully understood until Isaac Newton (1643-1727). More precisely, it is the product of the gravitational constant and the mass of the Sun that matters, and this product is now known with very high accuracy (11 decimal places). Based on hundreds of radar bounces from the surface of Mercury obtained between the 1960s and the present, the orbit of Mercury is known very well, but there remains an uncertainty in the position of perhaps a few hundred meters (1 part in a billion), in part because of the unknown topography of the planet. This uncertainty is now being considerably reduced because we can obtain many precise range measurements to MESSENGER, which is in orbit about the center of mass of Mercury, and because these measurements are not affected by the topography of the planet. So indeed with an improved knowledge of the position of Mercury will come an improved knowledge of its orbital period.

The orbit of Mercury is quite interesting because it provides an important test of Einstein's theory of general relativity, which has survived almost 100 years of experimental tests. The orientation of Mercury's perihelion (the point in the orbit closest to the Sun) is expected to change by a tiny angle over time (about 43 arcseconds per century). Although not a specific objective of the MESSENGER mission, the improved knowledge of Mercury's orbit can be used to refine tests of general relativity. Stay tuned for the results!

--Jean-Luc Margot, University of California at Los Angeles
MESSENGER Participating Scientist

The current theory of the origin of Earth's Moon calls for an impactor the size of Mars to have struck the Earth in the early years of the solar system. With its thin mantle and outsize core, could Mercury be a remnant of the impactor, having migrated closer to the Sun? - submitted by Kevin Schmida, Interested public, 05-29-2011

The giant impact hypothesis for the origin of the Moon has much of the Mars-sized impactor (including its iron core) merging with the proto-Earth. The material ejected by the collision formed a disc in orbit around the Earth, eventually coalescing to form the Moon, which is depleted in metallic iron compared to Earth.

 One of the big puzzles about Mercury is the origin of its proportionally large iron core. One way to explain this is a large impact that stripped off much of Mercury's crust and mantle. There are several other hypotheses for Mercury's formation. Hopefully, the measurements of Mercury's surface composition made by MESSENGER will allow the predictions of these hypotheses to be tested.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist


There is a lot of interst in naming features on Mercury. Given the IAU's theme for naming specific features on Mercury is to commemorate writers, artists etc., what are the chances of naming an entire region after the Mariner 10 probe? I refer here to the 'hilly and lineated' terrain antipodal to the Caloris Basin. As for commemorating MESSENGER, do we know yet where the highest peak on Mercury is?     Thank you and congrats on an awesome job! Bryce Johnson, Rockford, Illinois - submitted by Bryce Johnson, Journalist, 05-09-2011

The "artists and writers" theme for Mercury applies to impact craters. There are other themes for other types of features. For example, rupes (scarps) are named for ships of discovery, like the Santa Maria and the Beagle. However, the International Astronomical Union decided that spacecraft don't fit this theme. There may be other ways to honor Mariner 10 on the planet however, and we plan to explore them as the MESSENGER mission progresses.

MESSENGER is measuring topography on Mercury in two ways: with the Mercury Laser Altimeter, and via stereo images acquired by MDIS. There is not yet global coverage in these topographic maps. However, early indications are that the total relief on Mercury (difference between the highest place and lowest place, measured relative to a sphere of 2440 km radius) is considerably less than the total relief on the Moon, which is about 13 km. This is expected, because the Moon, having lower gravity, can support more extreme topographic lows and highs without undergoing collapse or "relaxation."

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

--Carolyn Ernst, Johns Hopkins University Applied Physics Laboratory
MESSENGER Geophysics Group

Hi! I have a question about the MLA, Is not sunlight interferes with this instrument? or did you find the appropriate wavelength, which does not emit the atoms that compose the Sun? - submitted by José Tejero Zapata, College student, 05-03-2011

The Mercury Laser Altimeter (MLA) emits pulses of energy at a wavelength of 1,064 nm. This wavelength is invisible to the human eye, but is well within the spectrum of light emitted by the Sun. MLA's receiver telescopes collect a portion of the energy pulse that is reflected off of Mercury's surface. When MLA ranges on the dayside, its telescopes will receive some amount of scattered 1,064-nm sunlight, which slightly decreases the signal-to-noise ratio of the data versus the equivalent measurement on the night side. However, the laser pulse is strong enough that this slight increase in noise does not pose a significant problem for the quality of the collected data. A bigger challenge faced by MLA is the highly elliptical orbit of MESSENGER. Because the intensity of the reflected signal decreases as a function of the fourth power of the distance between the instrument and Mercury, MLA is only able to range out to a
distance of about 1800 km from Mercury's surface.

-Carolyn Ernst, Johns Hopkins University Applied Physics Laboratory
MESSENGER MLA Instrument Team

Dear Sir,
press kit says on p.18 that Mercury has by far the highest density of the solid planets in our solar system, but generally it is said that it is (about) the same as Earth's density. Appears this has something to do with compressed (calculated?) or observed (actual?) density??? Can you please explain this and advise how to best write this understandable for laymen in my story? Would appreciate all your help in this!
Kind regards, Gerard van de Haar - entered by Q&A admin, 04-08-2011

The difference is whether one is referring to a planet's density in the strict sense, or to the "uncompressed" density.

If we simply take Mercury's mass and divide by its volume, the average density is 5.4 grams per cubic centimeter. In the same way, the Earth's average density is 5.5 g/cm3. However, the Earth is about 18 times more massive than Mercury. As a result, the great pressure deep in Earth's interior (caused by the weight of all the overlying material) causes the rocks of Earth's mantle and the iron in the core to be compressed. This increases the density. When this self-compression is accounted for, Earth's uncompressed density is about 4.0 g/cm3. Mercury, being so small, only uncompressed a little bit - from 5.4 to 5.3 g/cm3.

Thus to really compare the two planets, the numbers of interest are 5.3 g/cm3 for Mercury and 4.0 g/cm3 for Earth. The uncompressed densities indicate that Mercury's iron core is proportionally much larger than the cores of the Earth, Moon, Venus, or Mars. The volume of Mercury's core is about 42% of the volume of the planet. For Earth, this ratio is 16%.

Although the question of tidal forces possibly contributing to the heating of Mercury's liquid shell about its solid core was raised and discussed, I missed your view on this issue. Do you think the Sun plays a tidal force role in heating Mercury's core (as Saturn does with its moon Enceladus)? Earle Kyle. - entered by Q&A admin, 03-31-2011

Because of Mercury's eccentric orbit, there is a variation in solar tides on the 88-day period of Mercury's orbit about the Sun, but what we don't know are the interior characteristics that govern the dissipation of tidal energy to convert it to heat. One recent theoretical study explored the question of whether tidal dissipation in an outermost core just at the melting temperature could maintain the region in a fluid state, but the authors concluded that the uncertainties in key parameters prevent a definitive conclusion.

--Sean Solomon, Carnegie Institution of Washington
MESSENGER Principal Investigator

What is the evidence that Mars has a liquid shell surrounding its solid core, and what is the speculation as to what lighter elements are in this liquid mixture to prevent it from solidifying? Earle Kyle. - entered by Q&A admin, 03-31-2011

The evidence for a liquid outer core on Mars comes from tidal measurements. I've attached one of the principal references. There has been speculation for years over the mix of light elements in Earth's core, with S, Si, O, H, and C all proposed. For Mars, the menu is just as extensive.

--Sean Solomon, Carnegie Institution of Washington
MESSENGER Principal Investigator

 How efficient is the process for conversion or rotational to magnetic energy, and is it different for each planet (e.g. Mercury, Earth, Jupiter, Saturn)? Earle Kyle

We don't have firm answers on the efficiency of the power sources for dynamos in the planets. There are theoretical dynamo models for each — and multiple, competing models for most. The efficiency must, of course, be less than 100%. For Earth, many potential power sources are only marginally able to satisfy conditions amenable to a dynamo, so a high efficiency is implied for if those power sources are correctly identified.

--Sean Solomon, Carnegie Institution of Washington
MESSENGER Principal Investigator

Because Mercury is closer to a rotating Sun, it is experiencing time dilation, and length compression. The entire Mercurian system (planet and new artificial satellite!) with respect to our point of view is experiencing those effects in an astronomically significant way, along with orbital precession.
These effects are barely noticeable as far away from the Sun as Venus (if for no other reason than Venus is closer to our orbit, and farther away from the Sun's gravitational well.)
Are measurements of time and position and velocity affected significantly enough to necessitate corrections to MESSENGER data (or tracking) over the 12-month primary mission interval?
Sincerely, Samuel D'Arcangelis, New Jersey
- entered by Q&A admin, 03-30-2011

The MESSENGER on-board clock is more than accurate enough for the mission, but it is not accurate enough to detect relativistic effects related to time. However, all the trajectory-planning and analysis tools do incorporate adjustments for the spatial effects of both special relativity and general relativity. The relativistic effects are important for both long-term drift and for short-term corrections. The Radio Science analyses, which use Doppler shifts in the RF communications to detect small accelerations of MESSENGER due to Mercury's non-uniform mass, are particularly sensitive to many small factors, including relativistic effects.

--Mark Perry, Johns Hopkins University Applied Physics Laboratory

MESSENGER Radio Science team

(see also another question about relativity in the Geophysics category)


I know that irregularities in the orbit of Mercury suggested that something was wrong with the Newtonian model of the universe and that relativity happily accounted for those. Did planners have to take into account relativistic effects when designing the MESSENGER mission? - submitted by Bob, College instructor, 03-29-2011

The MESSENGER on-board clock is more than accurate enough for the mission, but it is not accurate enough to detect relativistic effects related to time. However, all the trajectory-planning and analysis tools do incorporate adjustments for the spatial effects of both special relativity and general relativity. The relativistic effects are important for both long-term drift and for short-term corrections. The Radio Science analyses, which use Doppler shifts in the RF communications to detect small accelerations of MESSENGER due to Mercury's non-uniform mass, are particularly sensitive to many small factors, including relativistic effects.

--Mark Perry, Johns Hopkins University Applied Physics Laboratory

MESSENGER Radio Science team

(see also another question about relativity in the Geophysics category)


How does Mercury's magnetic field, combined with its high orbital velocity, interact with the comparatively denser solar wind (plasma)? - submitted by Ralph Ricketson, Interested public, 03-25-2011

Studying the interaction of Mercury's surprisingly strong intrinsic magnetic field with the solar wind flow is one of the key goals of the MESSENGER mission. We know that Mercury has an internal magnetic dynamo that generates a planetary-scale field. But we are not sure how this generation occurs. The magnetic field
around Mercury leads to a miniature (compared to Earth) "magnetosphere" which slows, deflects, and distorts the solar wind plasma flow as it impacts Mercury. As the question implies, the solar wind density at the location of Mercury (only about 1/3 the distance of Earth from the Sun) is easily 10 times higher than at Earth's location. Also as the question notes, Mercury is moving in its orbit around the Sun at a high angular speed so the solar wind flow is "aberrated" in its relative flow direction.

We have hints from Mariner 10 flybys of Mercury in the 1970s and from the flybys of Mercury by MESSENGER in 2008-2009 that the solar wind-magnetosphere interactions at Mercury are complex, highly variable, and immensely intriguing in their character. There are indications that Mercury is able to "extract" much more solar wind energy (relatively speaking) than other planets in the solar system (such as Earth) are able to do. It seems that Mercury is able to convert this extracted energy into magnetic bubbles and bursts of activity inside the magnetic tail of the planet. But now that we are safely in orbit around Mercury, MESSENGER will have the unique opportunity to quantify these assertions and answer the questions that have persisted for over three decades.

--Daniel Baker, University of Colorado

MESSENGER Atmosphere and Magnetosphere Group

Evidence indicates that Mars once had a magnetic field likely generated by a molten and rotating (outer) core. Current theories suggest that Mars' core has cooled and solidified eliminating its magnetic field due largely to the heat loss of Mars' relatively small size. Although Venus is approximately twice the size of Mercury or Mars, it doesn't have a magnetic field either. Theory suggests that the lack of Venus' magnetic field is due to its very slow rotation rate. Mercury is slightly smaller than Mars and it also has a rather slow rotation rate, so if the Mars and Venus theories are correct, they present two fundamental mechanisms or reasons why Mercury shouldn't have a magnetic field. However, Mercury still retains a weak magnetic field. Why? Is Mercury's core still molten and rotating? Is its magnetic field due to residual magnetism? Is Mercury being tidally flexed by the Sun, similar to Jupiter's moon Io, to enable it to retain internal heat? - submitted by Ralph Ricketson, Interested public, 03-25-2011

You have hit on several necessary "ingredients" for a planetary dynamo (internally generated magnetic field):
1. An at least partially fluid metallic core. Mercury has a large metallic core (inferred from the planet's high bulk density).  Evidence that the core is still partly molten comes from Earth-based radar measurements of tiny changes in the rotation rate that allow us to distinguish between a fluid and solid core.
2. Rotation: it turns out that all the inner planets rotate sufficiently fast to allow a magnetic field to be generated, so e.g., Venus' absence of magnetic field is not due to the planet's slow rotation. (This issue of slow rotation implying no magnetic field is a common misconception in text books).
3. An energy source to drive the fluid motions in the core: e.g. cooling of the planet. This is still not understood fully for Mercury, but the fact that Mercury still has a fluid core, means that the planet hasn't cooled completely.

--Catherine Johnson, University of British Columbia

MESSENGER Participating Scientist

When I remember back to my days studying physics, I recall being told
that Mercury's orbital precession rate was a significant test of Albert
Einstein's Theory of General Relativity. I am wondering if the orbital
dynamics of the MESSENGER spacecraft will provide scientists with a new
chance to examine this theory in closer detail. Perhaps, by examining
Doppler shifts of MESSENGER's radio transmission or by timing occlusions
of MESSENGER's orbit more information can be obtained.

Thanks, Joseph Spuller - entered by Q&A admin, 03-20-2011

There would have been a test of general relativity each time Mercury passed
behind the Sun due to the time delay of the transmission of the carrier
wave information due to the gravity field of the Sun. However, the beam
passes through a variable plasma close to the Sun, which also modifies the
signal. Had MESSENGER also had K-band transmission as well as X-band, the
two frequencies could have been used to solve for the plasma effects and
the relativistic time delay could have been discerned. Cost prevented a
K-band transmitter and receiver, so MESSENGER will not improve on the
measurements made by the Mars Viking landers in determining the relativistic
time delay. That experiment was highly successful, made Irwin Shapiro
famous, and confirmed Einstein's theory to, I believe, less than 1%.

--Stan Peale, University of California at Santa Barbara

MESSENGER Geophysics group

1) How will the libration measurements including the laser altitude ranging
instrument data complement or enhance the magnetic field and gravity field

2) What will that tell us about the interior state of Mercury and the
history of the planet?

Question from mrwmurphr. - entered by Q&A admin, 03-13-2011

Subtle changes in the orientation of the planet (so-called librations)
can be measured in several ways: from Earth-based radar observations,
from the gravity field, from laser altimetry data, or from
high-resolution images. It remains to be seen which technique will
provide the best estimates, and the MESSENGER team will combine all the
data sets for a robust answer. The importance of the libration
measurements is that they can show that Mercury's core is molten, and
also provide an estimate of the size of the core, a crucial constraint
on models of the interior of the planet. At the end of the MESSENGER
mission, we should know more about the core of Mercury than any planet
other than Earth.

Understanding the core of Mercury is important because the core
properties influence many aspects of this enigmatic planet: its high
density and interior structure, its thermal evolution over the age of
the solar system, its magnetic field generation, and its global
contraction that resulted in a pervasive pattern of scarps on the
surface. A molten core may also have facilitated Mercury's capture in a
strange orbital configuration in which it spins three times on its axis
for every two revolutions around the Sun.

-Jean-Luc Margot, University of California at Los Angeles

MESSENGER Participating Scientist

Questions that defy categorization!

For years NASA has been looking for water or life on another planet.Has NASA thought about an experiment to place one sample of sea water on mars and one sample of fresh water. This could be shot from a tube that would have a camera that would impaled the ground. Then see what happens over some years. I'm just the wondering type. - submitted by Dean Ferrell, Interested public, 05-09-2015

The twin Viking landers, which operated on the surface of Mars in the late 1970s, carried experiments that were specifically designed to look for signs of microbial life in the martian soil. The experiments included ones in which water or nutrients were added to a sample of the soil that had been collected with the arm/scoop. The gases in the chamber were monitored to see what was produced. The consensus is that the results were negative for signs of life. The presence of highly reactive soil created by exposure of the surface to ultraviolet light is thought by most workers to explain certain results that first seemed to indicate that metabolic products were being generated.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Who tweeted on behalf of the MESSENGER? - submitted by Matthew Vitticore, 05-01-2015

MESSENGER was designed with a highly capable central processing unit, and to our surprise, the spacecraft became self-aware shortly after launch in 2004. This consciousness allowed MESSENGER to follow the news and learn of the advent of Twitter. Having comprehended the importance of social media, MESSENGER began composing its own tweets. (joke)
MESSENGER's Twitter feed was handled by a member of the Education and Public Outreach team.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What will happen with messenger? Will it melt when it will be turned to the sun? Kind regards, a 16-year old student interested in science and space. - submitted by Antoine Blanpain, Middle school student, 05-01-2015

On April 30, 2015, the MESSENGER spacecraft collided with a small ridge on the surface of Mercury at a speed of over 8,700 miles per hour (13,900 kilometers per hour). The energy of the collision, approximately equal to the explosion of a ton of TNT, would have completely destroyed the spacecraft, and excavated a crater roughly 16 meters in diameter in Mercury's surface.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I wanted to thank all of you who worked the Messenger program. You have done a great thing there. The news reports and pictures of the probe 'diving' into Mercury were released as they happened today, news reports said. They showed the 'last' picture sent from the probe on the far side of Mercury the news report said. How did the radio signal- of the last picture received- if the probe was on the far side of Mercury? My assumption is that it might have been the last 'line of site' transmission. Could you clarify this for me? I thank you agin for the years of new data you have given to the world with this program. - submitted by James P. nagle, 05-01-2015

As explained in this just-posted Q&A, it was not possible to transmit "live" images as the spacecraft was headed to impact. You are correct that the impact took place on part of Mercury that at the time was not visible to Earth. The last picture is indeed the last one collected and transmitted - it was collected earlier in the day, several hours before the impact.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Will japan have moon rock samples and will those samples have higher gamma radiation than the 1960 s even temporary? - submitted by Steven Ryan, 04-29-2015

Samples of rock and soil from the Moon were returned by the U.S. Apollo astronauts during six missions between 1969 and 1972, and by three Soviet robotic Luna spacecraft in 1970, 1972, and 1976.
At present, I believe that the only definite plans to perform lunar sample return are from China. The robotic Chang'E-5 spacecraft is expected to land, collect about 2 kilograms of material, and return to Earth in 2017.
Lunar materials are not particularly radioactive (sources of gamma rays), any more so than terrestrial rocks or meteorites. Gamma-ray spectroscopy is a technique used to determine the composition of planetary surfaces. The gamma rays are produced by nuclear reactions caused by the interaction of cosmic rays with a planet's surface.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

May I assume someone is going to adapt Spock's final quote?I have been, and always shall be, your Messenger. - submitted by Michael Milone, Ph.D., Interested public, 04-29-2015

Did Spock speak the acronym in all caps ("MESSENGER")? ;]

My school is doing a project where we have to find new life on a planet and my group chose Mercury. Is there anyway possible to have sustainable life on Mercury? - submitted by Lauren Fischer, High school student, 04-24-2015

Mercury is a pretty inhospitable place. There is no atmosphere (except for the highly tenuous exosphere), so the surface is subjected to extremes of heat and cold. There is water ice and probably organic matter within areas of permanent shadow near the north and south poles. These permanent shadows are extremely cold - just a few tens of Kelvin above absolute zero - and therefore life as we know it could not exist. However, you might imagine that areas beneath or at the edges of the ice might be warmed by geothermal heat or weak sunlight and allow liquid water to be stable. Liquid water + organics + a heat source could = pre-biotic chemical reactions or even life. We need to send a spacecraft to land at one of Mercury's poles to investigate further!

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

 It has been ages since last I wrote, but I have been busy working out a "post-MESSENGER" effort to promote a follow-up mission. I am writing to introduce the Mercury Explorers Society of America. We are a Facebook group dedicated to the serious investigation of Mercury as a venue for space science, exploration and human settlement. We are seeking members with a desire to work on the issues facing Mercury exploration and settlement in the post-MESSENGER era. Our efforts aim at creating credible plans for the unmanned and manned exploration, and eventual settlement of Mercury. We hope you will accept our invitation to explore this exciting New World. We can be reached at:  PLEASE NOTE: "America" is misspelled in the address and Facebook does not allow corrections. But this link should connect you with our site. Regards, Bryce Johnson, MESA Admin.
  - submitted by Bryce Johnson, Journalist, 03-17-2015

It's great to know that there is a group of people in the global public who are interested in building on the foundation laid by Mariner 10 and MESSENGER. Best wishes for a successful forum for discussion of the innermost planet!

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Was an official NASA mission patch developed and released for MESSENGER?Thanks for your time! - submitted by Tim Hurt, Interested public, 01-06-2015

A design was created and some cloth patches and stickers were produced. I've never seen one of the cloth patches, so they must be pretty rare!  I will post a good-quality jpeg of the design as one of our Gallery images of the day, during the last week in January. So if you are interested, you can check the Gallery then.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Good Afternoon to all at the MESSENGER team.

Not sure where to put these but thought this section would be best.

1) Has the volcanic feature at 36.1 North 68.8 East to the NE of Rachmaninoff Basin and west of Copland Crater within Hokusai Quadrangle been imaged at higher resolutions due to the periodic lowering of MESSENGER's periherm over the northern hemisphere? The highest resolution image I have seen is still the 26 metre resolution one, released a while back. Has any new information come to light as to when it may have last erupted or indeed if it is dormant or even active?

2) Regarding the permanently shadowed polar craters. I understand that these are not as cold as those on the Moon, yet before hand it was considered that the hermean polar craters would be far colder than the Moon's minus 240 Celsius /  minus 400 Fahrenheit equivalents. With mercury's denser crust I would have thought the hermean polar craters would be colder despite Mercury's proximity to the Sun. What gives? The solar wind?

3) Regarding the beautiful MDIS WAC enhanced colour images and mosaics, have the colours been identified with certain minerals and has a mineral map of the surface of Mercury been compiled. If so, are there unusual concentrations as i did understand that the southern hemisphere Rembrandt Basin was very rich in Iron.  

4) Has there been any evidence during the extended mission of former mercury moons been deorbited and impacted like Phobos will do with Mars? i know I had asked this over a year ago, just wondered if any new evidence or lack thereof has emerged.

5) Have the craters on Mercury pinpointed to different families of impactors or has it been random. I.E former Kuiper Belt Objects, Oort Cloud Comets, Main Belt Asteroids dislodged by Jupiter, etc?

6) Has the ratio of heavy Water against regular water been meaured in the ice or vapour over the plar regions in light of the recent news regarding the Comet 67P Churyumov-Gerasimenko three times Earth abundance of Deuterium from the ESA Rosetta Spacecraft / Philae Lander?

7) Any more news from the MESSENGER observations of comets 2P/Encke and Oort Cloud comet C/2012 S1 ISON?

I know it's me again and Thank You.

Andrew R Brown. Ashford, Kent, United Kingdom.

- submitted by Andrew R Brown, Interested public, 12-12-2014

1. The volcanic vent NE of Rachmaninoff was targeted by the MESSENGER observation planning team for a special set of oblique NAC images. The set was obtained on Nov. 27, 2014. The pixel dimension of this set is about 15 meters. We plan to release this spectacular mosaic through the image Gallery website. So keep your eyes on the Gallery!
2. The temperature in areas of permanent shadow is mostly determined by the amount of indirect illumination that is reflected into the shadow by high-standing topography. For example, the rim of a crater could scatter some sunlight into the permanently shadowed floor, raising the temperature. Since Mercury is closer to the Sun, the intensity of such indirect illumination is greater than at the Moon. Hence the coldest temperatures inside an area of permanent shadow on Mercury are higher than those on the Moon. The differences in the composition of the rocks (and hence small differences in thermal conductivity) between Mercury and the Moon would not be expected to have a major effect on the temperatures. Note that temperatures on the Moon have been directly measured by the Diviner thermal-infrared radiometer instrument on the Lunar Reconnaissance Orbiter spacecraft. Temperatures on Mercury have been modeled using the topography of the surface, knowledge of Mercury's orbit about the Sun, and assumed parameters (like thermal conductivity and emissivity) for the Mercury surface rocks. The same kind of models match the Diviner observations very well when applied to the Moon, so we have good confidence that the model temperatures for Mercury are close to the truth. But MESSENGER does not carry a thermal-IR instrument that can actually measure the temperature of the surface. The MERTIS thermal-IR instrument that will observe Mercury from the European BepiColombo Mercury Planetary Orbiter should tell us more about temperatures on Mercury.

3. Frustratingly, the reflectance spectrum of Mercury's surface is almost totally featureless in the wavelength range from ultraviolet (UV) to near infrared (NIR). This is the range where the MESSENGER camera (MDIS) and spectrometer (the UVVS and VIRS components of MASCS) are sensitive. The Moon, Mars, and some asteroids exhibit absorption bands in the UV to NIR that are mostly caused by iron in silicate minerals. But as has been shown by MESSENGER's Gamma Ray Spectrometer and X-Ray Spectrometer, there is very little iron in Mercury's silicate surface rocks (less than about 1-2% by weight). Rocks from the lunar highlands might have 5-6 wt.% iron (expressed as FeO content), and the volcanic mare basalts can have as much as 20 wt.% FeO. The UV to NIR spectral variations on Mercury mostly consist of differences in overall reflectance (that is, brighter terrains and darker terrains) and some variation in the spectral slope, with no clear absorption bands. Over the MDIS and MASCS spectral range, Mercury's reflectance increases with wavelength, a characteristic called a "red" spectral slope. Some features (like hollows, fresh crater rays, and the low reflectance material (LRM) are less red than the global average. Hence we can enhance the real color differences of the mercurian surface to create the color maps that you have seen. But we can only make inferences about the types of minerals that are present, based on the elemental abundances determined by XRS and GRS. A sample from Mercury would provide ground truth that would really help to understand the elusive planet! The BepiColombo MERTIS instrument should provide information on mineralogy by obtaining emissivity spectra. The spectral features in the thermal infrared are not so dependent on iron as are reflectance features in the UV - NIR.
4. I am not aware of any suggestion of a class of oblique impact craters that may have been formed by de-orbiting satellites of Mercury. However, one tiny such crater will be forming in late March or April of 2015: the impact of the MESSENGER spacecraft! 

5. Planetary scientists have identified two populations of impact craters on the inner planets (Mars, Moon, Mercury) . The first (older) "Population 1" impactors are related to the Late Heavy Bombardment, caused by the effects of Jupiter's gravity on the asteroid belt as the giant planet's orbit moved inwards toward the Sun at about 3.8-3.9 billion years ago. The major lunar impact basins and Mercury's Caloris basin were formed by Population 1 objects. The younger Population 2 craters are mostly the result of impacts by smaller objects from the asteroid belt that are nudged into planet-crossing orbits by the Yarkovsky force. Two publications that discuss Mercury's cratering record were written by Bob Strom and colleagues: R.G. Strom and colleagues (2011), Mercury crater statistics from MESSENGER flybys: Implications for stratigraphy and resurfacing history, Planetary and Space Science, 59, 1960-1967; and R.G. Strom and colleagues (2008), Mercury cratering record viewed from MESSENGER's first flyby, Science, 321, 79-81.

6. MESSENGER does not carry any instrument (such as a mass spectrometer) that is specifically designed to measure the isotopic composition of an ingested sample (such as dust or vapor). Dust and vapor are obviously of great interest with regard to comets, so the Rosetta orbiter and lander payloads do include instruments to measure isotopes.

7. Preliminary results from MESSENGER's comet observations were reported at the 2014 Lunar & Planetary Science Conference (Vervack, R. J., and colleagues, Results from the MESSENGER imaging campaign of comets C/2012 S1 (ISON) and 2P/Encke, Lunar Planet. Sci., 45, abstract 2585, 2014). The analysis is ongoing, and the team is also the spectra and images for comet C/2013 V5 (Oukaimeden) that were obtained by MESSENGER in September/October 2014.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Will the Messenger spacecraft at any time search for objects such as Vulcanoids orbiting close to the sun or perhaps Trojans that share Mercury's orbit (specifically the Lagrangian L4,L5 points) or perhaps looking within the vicinity of Earth for asteroids that from Earth would be difficult to locate? (due to the sun's glare) Thanks for any information you can provide. - submitted by john perry, 09-30-2014

A few questions about vulcanoids have been raised previously; go to the MESSENGER Q&A page and enter 'vulcanoid' in the search box to see the questions and answers.

It is important to keep in mind that MESSENGER's camera (MDIS) was designed to look at the Sun-lit surface of the planet, not distant and faint astronomical objects. Nonetheless, some improvisations have permitted searches for vulcanoids and moons of Mercury to be conducted.

1) For vulcanoids and satellites, we have performed several searches. With each successive search, we tried to improve the technique to boost our sensitivity, based on experience with the prior searches.

 None of the searches, either individually, or combined, were ever designed to be complete down to some fixed size. For vulcanoids, we were restricted to looking only at the outer portion of the cloud (due to pointing restrictions too close to the Sun). And even in the outer part of the cloud, we would have needed all opportunities to get nearly complete coverage. Due to other priorities in the mission, we did not get all the opportunities we originally proposed (nor did we expect to).

 In particular, for vulcanoids, we made some observations during approach to Mercury, which were designed to be more complete, but to a larger (vulcanoid diameter) size limit. During orbit, we sacrificed some coverage to push to smaller sizes. No vulcanoids have yet been found. Much of the data have been analyzed, but not all. And we still have some additional data-analysis techniques to try.

We reported on the early vulcanoid search at a Division for Planetary Sciences meeting in 2008:

Merline, W.J., Chapman, C.R., Solomon, S.C., Chabot, N.L., Gold, R.E., Hawkins, S.E., Robinson, M.S., A Program to Search for Vulcanoids from MESSENGER, DPS 2008, Bull. AAS 40, 491 (2008).

The entire vulcanoid search story will appear in a forthcoming publication.

2) For satellites, we had a much more complete search planned for the third Mercury flyby (M3), but the spacecraft safing event prevented that search. We had to regroup and come up with a more limited search from orbit. This is because, instead of looking at the entire system from a distance, we are now 'inside looking out', so it would require an excessive number of images to do a complete search.

Again, we have improved the satellite search technique with each new attempt. Much of those data are analyzed, but we continue to work on it and will be trying some new methods. No satellites have been found at this point. We will write a separate paper on the satellite search, including all of the data.

3) Mercury Trojans:  We considered this, along with possibly a search for IEAs (inner-Earth asteroids, objects that remain within Earth's orbit, and hence would be hard to see from Earth, but easier from Mercury). In fact, some researchers had inquired as to whether MESSENGER could search for specific IEAs that they had predicted might exist. But the small telescope aperture of MDIS meant that it would have been a difficult observation (and like finding a needle in a haystack).

There are a number of reasons that we did not pursue Mercury Trojans or IEAs:

A) None of these observations (including vulcanoids or satellites) were in the original mission plan, so any images taken were in a sense 'gifts' to us, and we felt to some extent we could not press overly hard to request additional observations that would detract from the mission's goals of studying Mercury itself. There were limited resources, in data downlink capacity, and particularly in personnel for planning observations. We also have limited resources for analysis. So we decided to put all of our eggs into the vulcanoid and satellite baskets, and focus more on those.

B) We have the impression that there has always been more interest in the possibility of vulcanoids than in either satellites, Trojans, or IEAs.

C) For Trojans, those objects would be easier to see from Earth than either satellites or vulcanoids, so our vantage point from Mercury was less important than for vulcanoids/satellites.

D) Mercury Trojans have been studied through dynamical models and have been found to be exceptionally unstable, much more so than Trojans of Venus, Earth, or Mars. So the likelihood that they exist is small. (That doesn't mean we shouldn't search, but with limited resources, we had to make some choices).

  E) The reason is NOT that Mercury Trojans would be too close to the Sun. In angular terms, the separation from the Sun would be roughly 60 degrees, well outside the camera's pointing constraints toward the Sun (although we never actually tried to plan a sequence, so it may be there are other pointing constraints that would come into play).

---William Merline, Southwest Research Institute
MESSENGER Science Team Associate

Hello,I have a couple of basic questions:- 1. What are the countries that organized the mission of the Messenger ? 2. How much did this project cost ? 3. What were your specific researchpossibilities ?thanks for your time - submitted by Gilles Vercruysse, Middle school student, 09-22-2014

1. MESSENGER is a mission of the National Aeronautics and Space Administration (NASA) of the United States. Certain spacecraft components were supplied by companies in other countries, and three members of the science team are from outside the U.S. - refer to the team page.

2. See this answer to a previous question.

3. The major goals of the mission are listed here.

--Dave Blewett, Johns Hopkins University applied Physics Laboratory
MESSENGER Participating Scientist

what are the mission dangers? what technology were used? what were the data collected? what is the exporation method? what is the mission objective? - submitted by lavinia cagilaba, Middle school student, 09-09-2014

You can find a vast array of information related to these questions on the MESSENGER website. In particular:

What are the mission dangers?, See ../About/Spacecraft-and-Instruments.html#thermal-design

What technology were used? See this page.

What were the data collected?, See ../About/Spacecraft-and-Instruments.html#instruments, ../Explore/Images.html#of-mercury and

What is the exploration method?, See ../About/Mission-Design.html

What is the mission objective?, See ../About/Why-Mercury.html

Hello - I am interested in whether or not Messenger was designed to detect non-thermal radio emissions from Mercury and, if so, if it detected anything. I know that thermal emissions were measured in the 1960s but i am interested in non-thermal. I understand Mercury has a tiny magnetic field and associated magnetosphere. If it does produce radio emissions, they likely are low frequency (long wavelength) and probably trapped by the magnetosphere and not detectable except by a very close fly-by. Did Messenger hear anything? If so, can you point me to reference papers describing what it heard? Thanks! - submitted by Whitham D. Reeve, 05-14-2014

 You can see a brief overview of MESSENGER's instruments at this link. None of the instruments are designed to measure radio emissions. Particles in the magnetosphere and exosphere are measured with the Energetic Particle Spectrometer and the Fast Imaging Plasma Spectrometer. The planet's magnetic field is sensed by the magnetometer.
Mariner 10 carried an infrared radiometer that measured thermal infrared emission from the surface, though at much shorter wavelengths (11 and 45 micrometers) than radio frequencies.

The Mercury Magnetospheric Orbiter portion of the European-Japanese BepiColombo mission to Mercury will carry an instrument for the measurement of radio emissions related to the magnetosphere.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Are there MDIS NAC imagery of both Comet C/2012 S1 ISON and Comet 2P/Encke at closest approach to Mercury. Have the rotation rate and orientation for the nucleus of Comet 2P/Encke been determined yet? A huge shame that C/2012 S1 ISON did not make it to perihelion though. Did MESSENGER get good spectra of both comets? Andrew Brown, Kent, UK. - entered by Q&A admin, 04-07-2014

MESSENGER conducted an extensive observing campaign of both C/2012 S1 (ISON) and 2P/Encke from late October to early December (ISON observations ended in late November of course). The campaign included over 700 comet images using both the wide-angle and narrow-angle cameras, as well as spectra at ultraviolet, visible, and x-ray wavelengths. The majority of the observations were successful, although most of the x-ray observations were severely affected by a series of solar flares at the time and unfortunately yielded no useful data on ISON. Many excellent images and spectra were obtained and are currently under analysis.

--Ron Vervack, Johns Hopkins University Applied Physics Laboratory
coordinator for MESSENGER comet observations

Hi, I'm a 18 year old college student from Brazil. My question is... what has Messenger discovered there that Mariner 10 missed?  Gabriel Amarante. - entered by Q&A admin, 03-11-2014

Mariner 10 did a fantastic job, considering the limitations of its trajectory (three flybys, did not go into orbit around the planet) and the technology of the early 1970s.

MESSENGER also performed three flybys of Mercury, but then entered orbit to carry out systematic studies. The orbital phase of the mission began in March of 2011 and will continue until March, 2015. If you look at the MESSENGER publications page, there are dozens of scientific papers that report on results from MESSENGER's observations of Mercury. So you could say that all the knowledge contained in those papers constitutes "what Mariner 10 missed".

The most obvious accomplishment of MESSENGER is that the cameras have been able to map the entire surface of the planet. Mariner 10, because of the timing of its flybys and of Mercury's rotation, was able to see only about 45% of the planet's surface (the same side of the planet was in daylight during each of the three flybys). MESSENGER's camera system can collect images using filters that select 11 different wavelengths of light in the visible and near-infrared. Mariner 10 collected only limited color images, in just a few colors. Therefore the MESSENGER images reveal much more about the color variation on the surface (color is related to the composition of the rocks). And since MESSENGER is in orbit, it has the opportunity to obtain much higher resolution images than did Mariner 10. These images (from the Narrow-Angle Camera) reveal finer details of the surface, and hence provide a better view of the geology. Even more detail about the color of Mercury's surface is measured by MESSENGER's MASCS spectrometer; part of MASCS is specialized for determining the composition of Mercury's super-thin atmosphere (exosphere).

Other major accomplishments: Mariner 10 did not have a laser altimeter to make precision measurements of the topography of the surface. Mariner 10 did not have X-ray, gamma-ray, or neutron spectrometers, which allow the elemental composition of the surface to be measured. Because MESSENGER is in orbit, its magnetometer has been able to map out the planet's magnetic field in much more detail than did Mariner 10. MESSENGER has instruments that measure particles in Mercury's magnetosphere, providing information on the interactions between the planetary surface, the magnetic field, and the solar wind.
As I mentioned, MESSENGER's findings have been reported in scientific papers. You can also read about many of MESSENGER's discoveries in the mission's News Archive.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

when a mixture of water and mercury is rotated about a vertical axis mercury moves away. why? - submitted by Vignesh, High school student, 03-10-2014

Mercury (the planet) and mercury (the silver-colored metal that is liquid at room temperature) are quite different things. But I expect that the answer to your question is that mercury metal has a much higher density than does water. Therefore, the mercury is able to displace the water when they are subjected to centrifugal force by rotating the container.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

1. How did water ice get onto Mercury?2. Is there any chance of life in the organic material near the water ice? - submitted by Katie, Elementary school student, 02-15-2014

1. You can read a summary of the evidence for the existence of water ice and organic material in permanently shadowed areas near Mercury's poles here. Comets and asteroids have been colliding with Mercury (and the other planets) since the beginnings of the Solar System, over 4.5 billion years ago. Comets are frequently described as "dirty snowballs", that is, they are composed of ices, rocky matter, and organic material. Asteroids can also contain minerals and rocks that include water-bearing minerals and organic compounds. Hence, when an asteroid or comet strikes Mercury, some of the water or organic matter may survive and migrate to locations where temperatures are low enough for the water or organic matter to stick. Certain impact craters in the polar regions are deep enough that the Sun never shines directly into the bottom. These permanently shadowed areas are extremely cold, and hence water ice and organic material can become trapped there for billions of years.
2. Life as we know it requires liquid water. However, because Mercury's atmosphere is so extremely thin, the pressure is to low for liquid water to exist on Mercury's surface or in the subsurface. Therefore, it is unlikely that any kind of living organisms could have evolved under these conditions.

--Dave Blewett, Johns Hopkins University Applied Physics Lab
MESSENGER Participating Scientist

How many astronauts have landed on Mercury? - submitted by diva rose, 01-14-2014

No person or robotic spacecraft from Earth has ever landed on Mercury. Robotic vehicles have landed on the Moon, Mars, the asteroids Eros and Itokawa, and Saturn's moon Titan.

Humans have visited only one celestial body: the Moon. Between 1968 and 1972, the American Apollo program made nine trips to the Moon. Apollo 8, 10, and 13 orbited without landing, and Apollo 11, 12, 14, 15, 16, and 17 landed at locations on the Moon's near side. Each Apollo spacecraft carried three people to the Moon. During the landing missions, one astronaut stayed in the orbiting Command Module while the other two descended to the surface in the Lunar Module. Three astronauts (James A. Lovell, John W. Young and Eugene Cernan) made two trips to the Moon, so a total of 24 astronauts flew to the Moon. A total of 12 astronauts have walked on the lunar surface.

Hopefully there will be a decision by various national space agencies to return humans to the Moon, and use the experience to enable an outward expansion so that people may explore asteroids and Mars. However, a human mission to Mercury is unlikely to happen for a very long time.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Good Afternoon to all at the MESSENGER team. Not a question rather a congratulations. The images released today of comets 2/P Encke and C/2012 S1 ISON are just incredible and with the MDIS WAC too. In fact they are good enough to have been taken from a dedicated comet spacecraft & MESSENGER just continues to deliver, not just with Mercury, but also with objects utterly alien to what MESSENGER was designed for. Hope you release some NAC frames too soon. I have followed MESSENGER as you know since well before launch and the mission never disappoints. - submitted by Andrew R Brown., Interested public, 11-25-2013

Thanks for the kind words, Andrew. The science and operations teams worked very hard to make MESSENGER's comet observations possible. The camera system was designed to look at the surface of the planet, not distant and faint astronomical objects, so the data is not optimal. But given MESSENGER's special viewpoint on these two exciting comets, it was decided that scientifically useful observations could be made and hence the project dedicated the resources needed to accomplish the goals. It turns out that data processing techniques used in the search for Mercury moons and Vulcanoid asteroids were important in allowing team members to rapidly analyze the comet images.

--Dave Blewett, Johns Hopkins University Applied Physics Lab
MESSENGER Participating Scientist

I once saw an article about water ice on Mercury, and forwarded it to friends. Can’t find article now. Do you have a copy? Jim Sanders - submitted by Jim Sanders, Interested public, 10-14-2013

The confirmation of water ice in permanently shadowed craters near Mercury's north pole generated quite a bit of press interest. For example, go to the "In The News" section of the MESSENGER website and scroll down to Nov. 29 to December 4 of 2012. No doubt there were other articles in magazines and newspapers.

For the actual scientific journal articles that relate to the water ice, check out these publications (listed on the Publications page).

Nancy Chabot and colleagues, Journal of Geophysical Research: Planets.

David Lawrence and colleagues, Science.

Greg Neumann and colleagues, Science.

David Paige and colleagues, Science.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

I want to know which gases are present in the planet Mercury? And their percentage? - submitted by Bhuvanahandu, High school student, 07-19-2013

The exosphere of Mercury is known from ground-based observations to have sodium, potassium, and calcium in it, and both hydrogen and helium were observed by Mariner 10 during its flybys of the planet. Of these exospheric constituents, MESSENGER regularly observes sodium, calcium, and hydrogen as it orbits Mercury. Potassium is too weak an emitter at the wavelengths MESSENGER can observe, and helium is outside its wavelength range altogether. MESSENGER has added magnesium to the known exospheric constituents and has made a very weak detection of oxygen. These are the known constituents of the neutral exosphere. Others have been searched for, including aluminum, iron, and sulfur, but thus far they have not been detected by MESSENGER.

It is not possible to discuss Mercury's exosphere in terms of percentages as one can for a thick, well-mixed atmosphere such as the Earth's. Mercury's exosphere is variable in both location around the planet and with time owing to its constant generation by a variety of variable source processes. As such, the number of atoms of one constituent relative to another is always changing. It is safe to say that the known constituents are some of the most abundant components of the exosphere, but others that are simply more difficult to detect may still be present at non-negligible levels.

--Ron Vervack, Johns Hopkins University Applied Physics Laboratory
MESSENGER Atmosphere and Magnetosphere Discipline Group

I would like to know if there is any volunteering opportunity with Messenger?Thanks! - submitted by Arshang, 05-16-2013

A Mercury version of the "Moon Zoo" citizen science project is under development. All MESSENGER data is freely available in the NASA Planetary Data System, so anyone with an internet connection is welcome to dive in.

College students may be interested in summer intern opportunities at the Johns Hopkins Applied Physics Laboratory. Typically there are several MESSENGER science- or engineering-related projects each summer. The application deadline is in January.

There may be additional opportunities for high school or college students who are local to the Applied Physics Laboratory (Laurel, Maryland, USA) to work during the school year.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Is there any chance for the astronauts to conduct exploration missions closer to mercury in the future? I have chosen my destiny as an astronaut, will there be any chance to land on mercury?(with the help of future technologies) - submitted by Alison, Middle school student, 04-21-2013

It's fantastic that you have set your sights on becoming an astronaut. There would be amazing opportunities for humans to carry out geological and solar physics research from a base on Mercury. However, it is unlikely that people will venture to the innermost planet any time soon. The dynamics of getting to Mercury are very difficult. Even sending a robotic lander to Mercury would be challenging (you can read a top-level study for a Mercury lander that APL conducted at this link.) A robotic sample-return mission would be even more expensive and technologically challenging (and might take 12 years or more for the round trip). Hence, unless a new form of propulsion is invented, or the world's governments dedicate trillions of dollars for a human mission using conventional rockets, there will not be any footprints in the
regolith of Mercury. Therefore, when you are in astronaut training, it is likely that you will be working toward a mission to the Moon, an asteroid, or Mars.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

On April 1st, 2013, Messenger took a photo of a geyser or eruption on the surface of Mercury. This feature was namedAvril Poisson, according to the blurb accompanying the photo. The blurb also mentioned possible future attempts to image the site on subsequent orbits. Question: Have you yet been able to acquire more imaging of this feature? If so, are the images available for general public viewing? - submitted by George Kendrick, Interested public, 04-20-2013

The MESSENGER Gallery image on April 1, 2013 was an April Fool's joke. Note that "Poisson d'Avril" is the French term for "April Fool." It is just a bit of fun in the spirit of our hoaxes from April 1 of 2012 and 2011. It is extremely unlikely that there is liquid water in the subsurface of Mercury.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What size and type of telescope or camera lens is used with the MDIS cameras? The description on the web page only says 10.5 degrees and 1.5 degrees field of view. - submitted by Brian Albin, Interested public, 02-23-2013

The details of the MESSENGER camera system (MDIS) are described in a paper by Ed Hawkins and coworkers published in 2007:
Hawkins, S. E., III, et al., The Mercury Dual Imaging System on the MESSENGER spacecraft, Space Science Reviews, vol. 131, 247-338.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Clearly MESSENGER is a "contrived acronym" to make a symbolic name, since Mercury is the messenger of the Roman gods. That's a "fact" do obvious I can't find a citation for it. It's just been deleted from Wikipedia for that reason. Could you supply some naming history or post it on your official site ? The last would satisfy Wikipedia's standards. Or point me to where this is published?There is a lot of stuff about how New Horizons to Pluto got its name (one not neary as good, IMHO). So can't you do the same for this splendid mission ? - submitted by Steve Harris, Interested public, 12-04-2012

It appears that the history of MESSENGER's name is not published anywhere. I got input from the Project Scientist, the Program Manager, and the Principal Investigator to piece together the following. Indeed, according to the supernatural beliefs of the ancient Romans, Mercury was the messenger of the gods. This association was used by Project Scientist Ralph McNutt in April or May of 1996 to craft the MESSENGER acronym we know and love today (MErcury Surface, Space ENvironment, GEochemistry and Ranging). According to Ralph, the name he put on the form to apply for APL internal development funds was "Orbiting Mercury Observatory". This was considered to be not catchy enough, so he played around with terms and the messenger god theme to come up with MESSENGER. He presented this at a meeting and everyone groaned, but no one was able to invent something better; hence the name stuck. Originally there was a colon after "MErcury". At one time, a Mercury mission named "Messenger" (just a name - no acronym) was proposed to the European Space Agency, though the MESSENGER team found out about this after selecting the name MESSENGER.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What i want to ask is not directly about Mercury but about the Solar System. Even so, because one major targets of Messenger Mission is to unveil how Solar System and rocky planets works, i think this question has some interest. As you know, Mercury has none or only a thin atmosphere. Even materials from his crust are volatized by the Solar wind (the holes who were discovery by this mission). Solar wind is too suspected to have ripped off the atmosphere from Mars because the planet doesn't have a significant magnetic field. So, how about Venus? He too doesn't have a significant magnetic field and he is closer than Mars. Why doesn't Solar Wind affect Venus atmosphere? It's because his atmosphere is constantly feed it? If the answer is yes, why Venus has so much energy and not cooled off with timing? Even so, why didn't we detected this occurrences in last past missions to this planet? I have to request some patience because is not your direct case of study. By knowing this fact, nevertheless, i thank you in advance if you reply my question. - submitted by Sergio Silva, Interested public, 11-07-2012

Mars and Venus both lack a global internally generated magnetic field, which would help to protect their atmospheres from stripping by the solar wind. You are correct that the atmosphere of Mars may have been significantly eroded by the solar wind. Mars has much weaker gravity than does Venus, so it is more susceptible to atmospheric loss in general. The atmosphere of Venus is being slowly stripped off by the solar wind, but the losses are small compared to the huge mass of the venusian atmosphere.

--Ron Vervack, Johns Hopkins University Applied Physics Laboratory
MESSENGER Atmospheres & Magnetospheres Discipline Group

What instruments and what information will be collected from Messenger? - submitted by Joe Bob Bearman, Middle school student, 10-18-2012

The MESSENGER website contains a wealth of material on the mission and the spacecraft. Especially look at this and this.

I am curious if you will be, or if you have already made any measurements of the solar energy? Specifically are you capable of measuring redshift of spectral lines from the Sun? I know Mercury is close enough to the Sun so that it's orbit needs to consider GR corrections, and I thought observing the redshift near Mercury could possibly convey some interesting facts.Thank you for your time,Mark - submitted by Mark Nelson, Interested public, 10-04-2012

The magnitude of spectral shifts in light as a result of the Sun's gravity and general relativistic effects are smaller than the spectral resolution of the MASCS spectrometer, which is 0.6 nanometer/channel in the range 115–600 nm, and 2.3 nm/channel out to 1450 nm.

This is a time dilation problem: a clock (or wave) in a gravitational potential would appear slow to someone watching from outside the potential. Someone from Earth looking at Mercury, which is deeper in the Sun's gravity well would see a clock (or a light wave) ticking away slower by about 1 part in 100 million. i.e., the frequency, viewed from Earth, would be lower by that much. But MESSENGER is deep in the gravity well along with Mercury. Looking from high altitudes down on atmospheric emissions near Mercury's surface will get a shift due to Mercury's gravity by a similarly small amount. A much bigger shift is the doppler shift due to the relative motion of the spacecraft and planet, but even that is too small to notice in the data.

--Timothy Cassidy, Laboratory for Atmospheric and Space Physics, University of Colorado, and Dave Blewett, Johns Hopkins University Applied Physics Laboratory

My question is how difficult/expensive would it be to design a mission in which we would send a nuclear powered rover to Mercury that would land in a crater that would provide protection from the sun?  I understand that there could be such locations on Mercury where there is actually water ice. Also, what would be the science potential of such a mission? - submitted by Daniel Kohn, Interested public, 09-07-2012

Certainly it would be extremely interesting to perform in-situ analysis of the material in the cold traps within mercurian permanently shadowed polar craters. The origin of the water (e.g., from asteroid or comet impacts, or produced by chemical reactions between the solar wind and the surface) are key issues. It would probably be best to try out technologies for operating in the extreme cold of the permanent shadow by first going to cold traps at the poles of the Moon.
The topic of a landed science mission has been covered here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

What was the messenger's first mission and results of the mission - submitted by Kevin agu, High school student, 09-02-2012

The MESSENGER mission was designed to answer six major questions. You can see descriptions of the primary and extended mission orbits.
The findings from the data returned by the spacecraft have been reported in a large number of conference abstracts and papers in the peer-reviewed scientific literature; here is the listing.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

1.what are the conditions in space that space engineers need to take into consideration when planning a mission 2.what does it take to launch a mission into space? (supplies,cost,etc...?) 3. What are the effects on space to the human body? - submitted by laura wotton, High school student, 06-14-2012

These are rather broad questions. [1]. The main challenges of designing a system for operation in space are the high vacuum and the thermal environment (any surface facing the Sun will become quite hot, any surface in shade could cool to extremely low temperatures). It is also necessary to design for the effects of microgravity (e.g., fuel will not automatically settle to the "bottom" of a tank). [2]. Space exploration requires money. The typically quoted cost of a Space Shuttle launch was about $1 billion. [3]. MESSENGER is a robotic mission, so there is no consideration given to the effects of space on humans. You may wish to begin your reading here:

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why is the MESSENGER mission important to scientists ? - submitted by kayla ortiz, Middle school student, 05-14-2012

The key questions that MESSENGER is designed to help answer are listed on the website, in the "Why Mercury" section.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

How much did MESSENGER cost? - submitted by Nathan, Middle school student, 05-10-2012

MESSENGER is a project in NASA's "Discovery" program, the "smallest" (lowest-cost) class of planetary mission. At the time that MESSENGER was selected by NASA in 1999, the cost cap for a Discovery-class mission was about $300 million. This includes building the spacecraft and the instruments, the cost of the rocket for launch, mission operations for the approximately six years from launch to orbit insertion plus the one-year primary mission in Mercury orbit, and support of the science team for data analysis and archiving.

--David Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Which planet is smaller than the Earth's moon? - submitted by Lalrem ruati, Middle school student, 04-30-2012

Mercury is the smallest planet in our Solar System. Mercury's diameter is about 4880 kilometers, which is larger than the diameter of Earth's Moon (3476 km). Pluto, an icy world in the outer Solar System, has a diameter of 2300 km, smaller than the Moon. For many years after its discovery, Pluto was considered to be one of the major planets in our Solar System. However new knowledge indicates that Pluto is a member of a vast family of objects in the outer Solar System known as the Kuiper Belt. Because it formed in a way that is fundamentally different from the eight main planets, Pluto is no longer considered to be a major planet. It is sometimes described as a dwarf planet. So the answer to your question is: There are no planets in our Solar System that are smaller than the Moon.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

Participating Scientist

Hello, how long will be the window for observing 2P/Encke from Mercury at the closest around the 18th December 2013? What will be then the shortest distance between MESSENGERand 2P/Encke? and the closest distance between Mercury and 2P/Encke? It seems that we might have a major opportunity to have a closer look at 2P/Encke with a much better view than we ever had from Earth, don't you think? What kind of measures could we get from MESSENGER about 2P/Encke in that window? thank you very much for your feedback. Kind Regards. - submitted by Hugues CAULIER, Interested public, 04-12-2012

MESSENGER is presently operating in its Extended Mission, which goes until March of 2013. If the spacecraft remains in good health and if NASA provides funding for a second extended mission, then observations of comet Encke in December 2013 may be possible. Comet Encke will come within 0.03 AU of Mercury. Images and spectroscopy should be possible. If the ion tail is directed toward Mercury at the time, MESSENGER's particle sensors may be able to sense the tail.

--Ron Vervack and David Blewett - Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientists

How long di it take to build the MESSENGER spacecraft? - submitted by karian, High school student, 04-11-2012

You can read the answer to a similar question here.


In an article where NASA satellite discovers natural mercury caduceus you put the picture with the date it was taken by the mission MESSENGER on March 31 2012, the image was taken by the Galileo spacecraft on August 28, 1993 and is the asteroid IDA in the background is the satellite Dactyl was discovered by johann Palisa, why put a fake image ? waiting for reply i need for my blog with the right information ASAP thanks ,,sorry for my English is not my language was translated by google. - submitted by JD, Interested public, 04-07-2012

The MESSENGER Gallery image release and caption for April 1, 2012 is an April Fool's joke. (As was the release on April 1, 2011). In many countries, there is a tradition of playing practical jokes on April 1.  See also this Q and A.

Concerned about the rush to land Mercury's new found moon on earth! Take issue with the risk being low, as mankind has never done this before! However, near earth would be better because it offers the reward of the mission paying for itself with the possible mining of helium-3! The earths magnetic field will strip it away and entry through the atmosphere for sure. Also estimated arrival at earth 2014? We don't know its surface hardness, or if the impact will be against a slope, and how will we track it when we crash the only craft near it! This is exciting to be sure, thank you for finding this moon. - submitted by DH, Interested public, 04-06-2012

The MESSENGER Gallery image release and caption for April 1, 2012 is an April Fool's joke. (As was the release on April 1, 2011.) The impact of a tiny spacecraft on a hypothetical moon orbiting Mercury would be far, far, far too small to push the moon out of Mercury's gravitational grasp and send it into an orbit that would cross that of the Earth. The image of "Caduceus" is actually the asteroid Ida, obtained by the Galileo spacecraft on its way to Jupiter in 1993. The names of the project personnel quoted in the gag article are joke names (see actual names of the MESSENGER team here). Note that the acronym for the Hermean On-surface Analysis with X-rays is HOAX, and the link is to last year's April Fool article about MESSENGER's encounter with "the Ancient Mariner (10).html".

Hi there --could Messenger possibly be visible from Earth? I 'm thinking by analogy to the Iridium flares, which can be visible during daylight because of the reflection from their antennas. I understand that Messenger's solar panels are 2/3 mirror; perhaps at its furthest distance from Mercury, the reflection might be visible from a telescope (maybe even an amateur telescope!) on Earth. Many thanks for your time! - submitted by Hugh Brown, Interested public, 03-10-2012

You raise a fun possibility. You could probably calculate the brightness of the glint from the panels and determine whether the glint could be visible at the Earth under the best circumstances. However, even if such a calculation were to suggest that a glint should be visible, in order to predict when a glint would occur, it would also be necessary to precisely know the position and orientation of the spacecraft and the orientation of the panels. But the exact spacecraft position and orientation are typically reconstructed afterwards from Doppler radio and star-tracker data. So I doubt it would be possible to know where and when to look.
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

When and where was MESSENGER developed? - submitted by Danielle, Middle school student, 02-28-2012

MESSENGER was built and is operated by the Johns Hopkins University Applied Physics Laboratory, in Maryland, USA. You can look at a map that shows the various US states and foreign countries that provided instruments, spacecraft components, or science team members.

In 1999 the project was selected by NASA based on a proposal to the competitive Discovery program. The spacecraft was launched in August 2004.

--Dave Blewett, Johns Hopkins University Applied Physics Lab
MESSENGER Participating Scientist

What is a light year? - submitted by Devontae Givens, Middle school student, 02-01-2012

A light year is a unit of distance (length) used by astrophysicists and cosmologists. It is equal to the distance that an electromagnetic wave (such as radio, or visible light) travels in a period of one Earth year. Light moves at a speed of about 300,000 kilometers per second in a vacuum. Thus, in a year, light travels a distance of about 9.5 trillion kilometers.

The Earth is about 8 light minutes from the Sun.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Dear Sir, According to Dr. David Morrison he says that comets are no more than a few kilometres across. If this is true how do you explain the alleged comet that bang our Sun causing massive explosions on our Sun? This incident took place on, October the first of this year (2011-10-01). Can you please explain to me the force needed to hit the Sun as it did? And could a comet of ice and a little iron be able to cause that explosions? Hope to hear from you soon. Respectfully yours, Sergio,II. - submitted by Sergio Correa,II., Interested public, 11-27-2011

I provide here a link to an explanation concerning the lack of evidence that Sun-grazing comets cause coronal mass ejections (CMEs).

-Ronald Vervack, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist


We just started the space unit of 9th grade physical science this week. We started with the Solar System and in trying to keep my lessons current, I brought in some of your findings from MESSENGER.  One of my students asked if there was any plan for a follow up mission to land a craft on the surface of mercury. I would imagine it would be a rough place for a rover type of craft, but perhaps something like viking that could land and obtain data from some of these hollows you have discovered and/or analyze the surface closer to determine a cause of the surprising high sulfur content? Thanks.  Wil Keepers, Willamette Valley Christian School, Salem, Oregon - submitted by wil, K-12 teacher, 11-11-2011

That is a great question, one we've received before. Check here for the answer.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

There have been Earth-based observations implying high concentrations of titanium in at least three regions on Mercury. Do we have data from MESSENGER for Titanium concentration?     Also, has the presence of chlorine ever been suggested in Mercury's atmosphere?   Thanks again for a terrific site! - submitted by Bryce Johnson, Journalist, 10-27-2011

The ground-based observations that found evidence for Ti in the mineral rutile (TiO2) at three large areas on Mercury's surface were based on the overall slope of the spectrum between 8 and 13 micrometers. The MESSENGER spacecraft with its X-Ray Spectrometer (XRS) has measurements that indicate no measurable Ti (an upper limit of less than 1 wt. %) at the locations measured.  The XRS measurements are more reliable than those based on the slope of the mid-infrared spectrum.  There has been suggestion that Cl could exist in Mercury's exosphere. The Mercury Atmosphere and Surface Composition Spectrometer (MASCS) has made observations designed to look for the emission line from that element, but it has not yet been seen.

Ann Sprague, University of Arizona
MESSENGER Participating Scientist

Could a cell phone affect us, as in making contact with messenager, i had mercury messanger installed in my mobile phone, ( its a message service ) while i am speculating if the satalite is bouncing off its strong magnetic energy back to earth, causing earthquakes. - submitted by may emerals, 10-24-2011

There is no connection between the NASA MESSENGER spacecraft (orbiting planet Mercury) and cell phones or a mobile messaging service.

The radio signals used by cell phones, radio and TV broadcasts, or in satellite communications cannot cause earthquakes.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

In regards to a Mercury directed Coronal Mass Ejection of Sept. 8th of this year (Sept. 9, 2011,, how did Mercury's magnetosphere react?Was the surface impacted by the CME?Also, how did the spacecraft perform during, and after the CME reached it? - submitted by Randy in Oregon, Interested public, 09-17-2011

The spacecraft experienced no problems. The magnetic field of this CME was not as dramatic as prior CMEs observed from Mercury orbit. Although the magnetic activity may have been enhanced by this CME, the impacts on the planetary surface were not dramatically greater than normal variability.

--Brian Anderson, Johns Hopkins University Applied Physics Laboratory
MESSENGER Deputy Project Scientist

Is there any book on MESSENGER's findings that brings together all the observations and theories? - submitted by Sriram, Interested public, 08-24-2011

Several publishers have contacted the project about a possible new book about Mercury. However, it is still to early to consider such an undertaking. Perhaps once MESSENGER finishes is primary mission in April of 2012 the team can turn its attention to a synthesis of our findings. By the way, the 1988 University of Arizona Press book on Mercury can be downloaded here.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Will there be any attempt by MESSENGER to image comet C/2010 X1 when it reaches or approaches perihelion? In looking at the trajectory visualization at JPL it appears that Elenin will pass much closer to Mercury than Earth.Thanks! - submitted by Jon in SC, Interested public, 08-18-2011

Comet C/2010 X1 Elenin disintegrated during its passage into the inner solar system and was not a viable target for observations. A much more favorable opportunity will be for comet 2P/Encke's very close passage to Mercury in November 2013, assuming that MESSENGER's mission is extended to that time frame.

Ron Vervack, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

On Twitter, I asked Messenger, "What caused the streak/canal/trough running from mid-image to the bottom of the image?" referring to ../Explore/Science-Images-Database/pics/EN0219038585M_cal_map.pngMessenger's reply on Twitter was, "I asked my scientists what they thought it was, and their response 'overlapping secondary craters form a continuous depression.'"I wasn't certain what that meant, so I followed up by asking, "Trying to wrap my head around that. Clarification? A link to explanation, perhaps?"Messenger suggested that I come here and ask you directly. What does "overlapping secondary craters form a continuous depression" mean? Could you possibly describe what happened?Thank you! - submitted by Tim B., Interested public, 08-03-2011

When an asteroid or comet strikes the surface of a solid body like Mercury, a tremendous amount of energy is released. The kinetic energy of the impactor serves to fracture, crush, melt, vaporize and eject a volume of rock at the target site, forming an impact crater (similarly destroying the impactor in the process). Some of the material that is ejected from the crater travels on ballistic trajectories and re-impacts the surface at a distance from the parent crater. These secondary impacts may also form craters. Sometimes a series of chunks of ejecta follow similar paths away from the parent crater and hit the ground in close succession, making secondary craters that partially overlap. A set of overlapping secondary craters thus may form an elongated valley-like depression. That is what you see in the image.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

An unscheduled radioactive Cs137 source has emerged on board MESSENGER, detected by the onboard gamma sensors. I would like to know where I can get more detailed information. When it was first detected, after which flyby. What is the energy of the detected gamma radiation.

In connection to its  origin, I would like to know if there are  in the spacecraft, components exposed to the solar  wind that contains Sn, such as galvanized steel or soldering. Thank you. - submitted by M. Dube, 07-21-2011

We first detected the presence of the 662-keV gamma ray line during early commissioning of the Gamma-Ray Spectrometer (GRS) instrument shortly after launch. We have attributed this energy line to a small amount of Cs-137 contamination that most likely resides in the materials used to construct the GRS itself, but it could possibly come from materials further away in the spacecraft. From the data we have in-hand, we cannot say for sure where the source resides since the signal is very weak (less than 5 counts per minute) and we did not detect it in our relatively short-duration ground tests conducted before the GRS was mounted on the spacecraft. We can say that the decay time is consistent with Cs-137 and that the intensity followed the predicted decay curve very precisely during 6 years of cruise, including all of the flybys.
We believe the source of the contamination is most likely within the instrument itself because any detected signal intensity from sources farther away will fall off as the square of the distance from the detector and those gamma rays would have to pass through the spacecraft, which can be highly attenuating at this energy. We also observed no deviation in the intensity as the spacecraft used up considerable amounts of fuel, which further supports the hypothesis that the contamination is close to the instrument. We may at some point conduct some long-duration ground tests on the backup unit to help answer this question more definitively.
In regards to your hypothesis for its origin (presumably a form of nuclear activation), most of the spacecraft components are contained within magnesium or aluminum housings and covered with thermal blankets (multi-layer insulation), all of which are meant to provide shielding from the solar wind as well as more energetic solar particles. In general, the space industry avoids the use of Sn because it tends to grow "whiskers" (dendrites) over time that can cause electrical shorts, etc., so we use specially-formulated solders.
Thanks for thinking about this puzzle.
--John Goldsten, Johns Hopkins University Applied Physics Laboratory
MESSENGER Gamma-Ray Spectrometer Instrument Engineer

Have you looked at the results from electric discharge experiments? I consistently get planetary-like features in my experiments with a dust covered CRT. - submitted by dz parker, 06-17-2011

According to one hypothesis, early in Solar System history dust grains in the solar nebula were melted by lightning-like electrical discharges, to form the small silicate spherules called "chondrules". Chondrules are one of the main constituents of primitive meteorites.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

We have a huge project about the MESSENGER mission and we are having troubles finding some information if you could answer these few questions that would be great!

1. What countries were involved in the MESSENGER mission?

2. Where did the money come from? How did you fund the whole mission?   THANK YOU SO MUCH!! please respond as soon as possible it will be greatly appreciated. - submitted by Leah Smith, Middle school student, 06-15-2011

1. You can find information about the team on the project web page.

2. NASA is a U.S. government agency that gets its funds from the taxpayers.
MESSENGER is a project in NASA's "Discovery" program, the "smallest"
(lowest-cost) class of planetary mission.

Good luck with your project!
--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why isn't Pluto considered a planet anymore? - submitted by Jessica benjamin, Middle school student, 05-27-2011

Pluto was discovered in 1930 by Clyde Tombaugh. In the ensuing years, several theorists postulated the existence of a belt of icy objects in the outer Solar System beyond the orbit of Neptune. This region came to be know as the Kuiper Belt. In 1992, David Jewitt and Jane Luu of the University of Hawaii discovered the first Kuiper Belt object (KBO) beyond Pluto. I had the good fortune to take a class on Solar System astronomy from Dave during my first year of grad school at UH. Since then, hundreds of KBOs have been found, and a number of them are about the same size or larger than Pluto. The spectral properties of the KBOs indicate they have similar compositions to Pluto, and several of them have moons. Thus it is clear that Pluto is a KBO, but just happens to be the one that is closest to Earth and was the first to be discovered. This puts Pluto in a different class of object than the eight regular planets.

It is not unusual to reclassify something when new knowledge is gained, whether the something is a Solar System object or a dinosaur skeleton. Revising our views in light of new evidence is what science is all about! For example, the first asteroid to be discovered, Ceres, was called a planet for about 50 years after it was spotted in 1801. But as more objects in similar orbits were discovered, scientists realized Ceres and its neighbors are distinct from the main planets. So we no longer refer to Ceres as a planet; it is an asteroid.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Is there a web page where all of the images being sent back are being stitched together into a global map?Examples:Google Earth Moon Google Mars there be something akin to Google Mercury? I'd love to explore these images together. Best wishes,Ken MacAllister - submitted by Ken MacAllister, Interested public, 05-26-2011

We have a way for you to view a MESSENGER flyby mosaic in Google Earth. A more formal "Google Mercury" release from Google may be available in the future. You might also want to check out the U.S. Geological Survey's Map-A-Planet website, where you can browse and download scientific images from throughout the Solar System.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

A) Would a magnetic field be necessary to maintain an atmosphere on Mercury? I read somewhere that the low gravity and the lack of a significant magnetic field is the main reason for 'outgassing' where any gases 'evaporate' into space without staying near the planet. B) If you were to go to Mercury for some length of time, what material would you need to bring? Assume for a moment we can get an abundance of solar energy so we can change local materials (for example generate O2 from local miniscule sources of H2O) and also assume that there is some ice in some crevises on the planet. Is there for example any carbon on the surface that could be used to 'generate' carbohydrates (whether artificial or by plants)?  C) Is there any part of Mercury that never sees sunlight? For example near the polar regions. - submitted by Andy, Interested public, 04-12-2011

A. Mercury has an internally generated dipole magnetic field, with a strength about 1% of Earth's. Mercury's atmosphere is extremely thin, and is classified as a surface-bounded exosphere. Because of the weak magnetic field and lack of a thick atmosphere, Mercury's surface is directly exposed to energetic particles from the solar wind and to impacts by micrometeoroids. Both the solar wind and micrometeoroids can cause vaporization of the surface materials that they strike. Some of the vapors are able to escape the surface and replenish the exosphere.

B & C. MESSENGER's solar panels harvest the intense sunlight for conversion to electric power. Silicate rocks contain abundant oxygen, but it is more tightly bound than the oxygen in water, so more energy is required to extract it. The floors of some craters in Mercury's polar regions are in permanent shadow and may contain water ice. The solar wind contains some carbon (it is mostly hydrogen), so a bit of carbon could be obtained by extracting implanted solar wind carbon from the soil.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Is Mariner 10 still in orbit around Mercury?? Or has it crashed somewhere?   Will MESSENGER get any "real" pics of Mariner 10 over the next year??  from John in Canada - entered by Q&A admin, 04-10-2011

Mariner 10 did not orbit Mercury; it made three flybys in 1974-75. Shortly after its third Mercury flyby in March, 1975, all the gas for the spacecraft's attitude-control jets ran out and contact with the spacecraft was lost. Mariner 10 is probably still in orbit around the Sun, but over 35 years of solar radiation pressure and possible gravitational encounters with Mercury (near or far) make it impossible to predict where the spacecraft is today. The odds of Mariner 10 returning to the vicinity of Mercury while MESSENGER is in orbit are small.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Hello , After playing around with Google Mercury, I found something you might like to see! I found an area that looks like a scary alien face with its mouth open. Here are the location numbers..... Feel free to name it after me !43*15'33.31"s - 101*18'50.41"e - submitted by Talan Morrison, College student, 04-08-2011

It's good that you are enjoying Mercury in Google Earth. We had some trouble seeing the monster that you perceive, but it is fun to look. The human brain is very good at trying to make sense of random patterns.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory
MESSENGER Participating Scientist

Why Orbit Mercury? Why is it not possible to land? If you can do all the communications from the orbit, you can do the same when it lands?Drop some heat-resitant rovers on to Mercury surface and then have a communication between the orbiter and the surface roveres - submitted by Ravi, Interested public, 04-06-2011

At the request of the National Academy of Sciences, the JHU Applied Physics Lab recently did a top-level study of what would be needed to place a lander on Mercury. Needless to say, it would be very challenging. The spacecraft would need to follow a path similar to MESSENGER's (5 or 6 years of cruise, with several planetary flybys), all the while carrying a large rocket motor for performing a soft landing. Perhaps a Mercury lander will become a priority after both MESSENGER and the European Space Agency's BepiColombo Mercury orbiters have completed their missions.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist


Was this picture of Mariner 10 an April Fool's joke??  Thanks, Henry Levenson - entered by Q&A admin, 04-02-2011

Yes. In fact, our gag made a list of best science-related April fool sites.

What are the surface temperatures of the night side of Mercury? Would landing a craft be possibilty in the future, especially if polar water is found? Also, at the end of MESSENGER's mission would it be possible for it to orbit the Sun and maybe acquire more data on our star? - submitted by Ali Shah, College instructor, 04-02-2011

Concerning a Mercury lander, look here.
To learn about the end of MESSENGER's mission, browse the Q&A section of the website, under the category "Orbiting Mercury." MESSENGER is a planetary science mission designed to investigate Mercury. MIssions intended to study the Sun carry very different suites of instruments, and are flown by NASA's Heliospherics Division.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Hi MESSENGER-folks! I admire your work - you are doing fantastic jobs! I will use your material in my English classrooms (all ages) with the help of my ibook and my video projector. Question: are there also videos / or animations available? I know signals travel a long way to our small planet. Fliegergruss from Wolfgang Pluemer (CTSW pilot) in Zierenberg / Germany - entered by Q&A admin, 04-01-2011

Wolfgang, It's great to have another international supporter. Have a look at all these resources:

-Two animations on the orbital operations page.

-Animations and the Visualization Tool for flybys one, two, and three.


and Mercury in Google Earth.

All of us on the MESSENGER team wish the best to BepiColombo.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

[this was passed to me, third hand, from someone at the Ok state health sciences center. It is hoped it will be ignored and not detract from our hope the Mercury will get the best possible presentation in the public view]

From Dr Dunderhead, head of the institute for terrible technology (ITT), I have, as an amatuer space enthusiast noticed a wonderful contrast in the public web pages of JHUAPL specifically in MESSENGER web logs, status messages, etc. and other NASA labs, JPL (pasadena) . JHU-APL'S uses status logs about MESSENGER to explain simple physics ideas behind space craft operations in practical ways. Its simplicity and focus have been a joy to read.

Is there someone who could elaborate on this JHU-APL journalistic style, preferrably without making fun some of my friends elswhere at NASA? One of the artists we know states western (calfornia) and eastern (new york) artistic cultures have differences, eastern very narrowly focused, western artists make their own world and worldview. The web authors of the MESSENGER site may deserve alot of credit and maybe that is all there is to the perceived difference. But it gave me the idea that maybe its because of the institutional style of JHU-APL, due to history, or service branch afilliation that differs from other labs?      Well, so much for Dunderhead. thanks, Robert - submitted by RobertInOKC, Interested public, 04-01-2011

It is April 1st, nonetheless this appears to be a compliment. We'll take it as such. Thank you.

On the images being released, one of the meta data blocks is the "Image Mission Elapsed Time (MET)".  Could you please explain what that exactly means. Thank you.
- submitted by Christian, Interested public, 04-01-2011

MET is the time, in seconds, since MESSENGER launched. It is used to identify the the instant at which the image was collected.

Do you believe that you'll find evidence of "Ice" on Mercury in shadowed crater regions? - submitted by Jim Stryder, Other educator, 03-31-2011

The nature of the polar deposits is one of the major questions that the mission is designed to answer. MESSENGER's neutron spectrometer will be looking for hydrogen in the polar regions as it gathers data on each orbit. Stay tuned!

Will we see photos of the Sun made by MESSENGER? Greetings, Dyl - entered by Q&A admin, 03-30-2011

MESSENGER is designed to investigate the planet Mercury, so its camera and other instruments are not able to look at the Sun. In fact, all the instruments and the spacecraft body must remain behind the sunshade to avoid overheating. (One exception is the X-Ray Spectrometer's solar monitor, which peaks through the sunshade to guage the Sun's output of X-rays. However, this is not an imaging instrument.) If you would like to see spectacular images of the Sun, search on the web for information about NASA's STEREO mission.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Are there any plans for an unmanned landing mission to Mercury? - submitted by Bryce, Journalist, 03-30-2011

At the request of the National Academy of Sciences, the JHU Applied Physics Lab recently did a top-level study of what would be needed to place a lander on Mercury. Needless to say, it would be very challenging. The spacecraft would need to follow a path similar to MESSENGER's (5 or 6 years of cruise, with several planetary flybys), all the while carrying a large rocket motor for performing a soft landing. Perhaps a Mercury lander will become a priority after both MESSENGER and the European Space Agency's BepiColombo Mercury orbiters have completed their missions.

--Dave Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist


Why don't you have a scale of km on your beautiful Mercury pictures?  Without a scale, they are very difficult to appreciate. Question from John McClure. - entered by Q&A admin, 03-20-2011

Every image in our gallery has a caption that includes the scale of the picture, for example

giving the diameter of the planet or the size of a feature shown in the image.

When you say that MESSENGER will fly by the Sun 15 times before it makes its approach to the inner planet, what is the inner planet? - submitted by Sally, Interested public, 03-20-2011

The "innermost planet" refers to Mercury, MESSENGER's target. Learn all about the trajectory here.

can you fill me in on any updates because i want to work for NASA when I grow up. on fact my teacher let me teach a class. - submitted by zach, Middle school student, 03-18-2011

Zach, Congratulations on being selected to teach a class. Keep checking back to the MESSENGER website for lots of images and other data as the mission progresses.

[a] What do you expect to find on the planet Mercury that could be important?

[b] Is there any chance there could be water on Mercury?

[c] What are you hoping to find that could tell you how the universe started?

[d] What kind of atmosphere does Mercury have?

[e] To me Mercury seems just like a hot planet and it would have nothing to offer. Do you think the cost of this mission is worth it based on what you expect to find?
 Thank you. - submitted by Danny, Interested public, 03-18-2011

[a] MESSENGER was designed to answer a set of fundamental questions about Mercury. As a New York Times editorial on March 18, 2011 said of MESSENGER's entry into Mercury orbit, "Part of the thrill is knowing that this is the pure pursuit of knowledge, the scientific impulse — a human impulse — carried to a remarkable conclusion. It's hard to know just what we will learn about Mercury. Like all scientific missions and experiments, this is a journey to a more refined sense of what we don't yet know."

So part of what MESSENGER will do is to satisfy natural human curiosity about our surroundings, whether those surroundings are behind the next hill, over the horizon, or orbiting close to the Sun. (If the ancestors of the Polynesians had stayed on the shore, they never would have discovered and populated Hawaii, Samoa, the Marquesas, Rapa Nui and the other islands in the Pacific.)

Just as importantly, a better understanding of Mercury's composition and history will lead us to a better understanding of the way that Mercury and the other planets (including Earth) formed and evolved. This in turn will inform observations that astronomers are making of the planet-forming process around other stars. We'd like to know how frequently small rocky planets (like Mercury, Venus, Earth and Mars) form around other stars.

[b] With daytime temperatures as high as 800 degrees F and next to no atmosphere, liquid water cannot exist on Mercury. Curiously, however, Mercury may have deposits of water ice hiding in permanently shadowed areas near the north and south poles.

[c] Well, perhaps not the Universe, but understanding this "end member" among the terrestrial (rocky) planets is crucial to learning how the all planets in our Solar System formed and evolved.

[d] Mercury has an extremely thin atmosphere (exosphere).

[e] We are fortunate to live in a wealthy nation that can afford to devote a tiny amount of its resources to pursuits of the imagination like scientific research, the arts and humanities. NASA consumes less than 1% of the Federal budget, and robotic planetary exploration is a small fraction of that. As mentioned above, comparative studies of the other planets provide knowledge that helps us to learn how our own Earth works. In addition to scientists, a mission like MESSENGER employs numerous engineers, programmers, and support staff. Space exploration drives development of new technology, and serves to inspire young people to consider schooling and careers in science, engineering, and mathematics. These young people grow up to be the next generation of technical leaders, helping to maintain our country's economic competitiveness.


--David Blewett, Johns Hopkins University Applied Physics Laboratory

MESSENGER Participating Scientist

Is there enough ice at Mercury's poles for future colonists to use and sustain themselves? Could they use any oxygen that might be in the soil to manufacture water and breathable air? Just wondering if explorers would have to take everything with them to survive, including all their own air and water. Thanks.

Question from thadamson. - entered by Q&A admin, 03-02-2011

Earth-based radar studies of Mercury show that certain areas near the poles have an unusual, high degree of reflectivity to the radio waves. Most of these areas coincide with the interiors of craters, and are locations that are permanently shaded from the Sun. As such, these areas are expected to be very cold, and could be places where water (delivered by comet or meteorite impacts) could collect in the form of ice. Indeed, the radar properties of the permanently shadowed craters are similar to those of the martian polar caps and the icy satellites of the outer planets. So it seems like a good bet that water ice is lurking in Mercury's polar craters, but we don't know for sure (deposits of sulfur could produce similar radar signatures). Discovering the identity of the polar materials is one of the major questions to be addressed by MESSENGER. The Neutron Spectrometer will be able to determine the abundance of hydrogen at the north pole. If high levels are found, that would be evidence in favor of water ice (which is composed of hydrogen and oxygen) being responsible for the unusual radar properties.

A recent radar study found an area of 7500 square kilometers of potential icy deposits within 5 degrees of Mercury's north pole (the depth of the deposits is less certain). Thus if humans were ever to venture to Mercury, there should be plenty of water to use. The water could also be split to obtain oxygen for breathing using electricity generated with the abundant, intense solar power available at Mercury. Rocks also contain major amounts of oxygen, but it takes much more energy to break the chemical bonds with silicon than it does to break water up into hydrogen and oxygen.

--David Blewett, Johns Hopkins University Applied Physics Lab

MESSENGER Participating Scientist

Why are only low resolution images available to the public and the Messenger website? - entered by Q&A admin, 10-04-2009

Actually, the images commonly released to the website are the full high-resolution images, directly as returned by MESSENGER with a minimal amount of processing. So these are the highest-resolution available. Additionally, all MESSENGER data from all instruments are publicly released to the Planetary Data System ( six months after each flyby. The PDS archives raw data as well as calibration information.So anyone with an internet connection can obtain as much of the data produced by the mission as they want. All NASA missions follow similar policies regarding release of data to the PDS.