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MESSENGER Press Conference Multimedia Page

Presenter #1
James L. Green, Director
Planetary Science Division, NASA Headquarters


Presenter #2
Sean C. Solomon, MESSENGER Principal Investigator
The Carnegie Institution of Washington

Image 2.1

Click on image to play the movie.




MESSENGER Approaches Mercury

On January 13, 2008, beginning 30 hours before MESSENGER's closest approach to Mercury, the Wide Angle Camera, part of the Mercury Dual Imaging System (MDIS), began snapping images as it approached the planet. Over this period, MESSENGER imaged the planet once every 20 minutes to produce this approach sequence, which has been compiled into a movie. At the start of the movie, the MESSENGER spacecraft is about 630,000 kilometers (about 390,000 miles) from Mercury. The movie ends when MESSENGER is about 34,000 kilometers (about 21,000 miles) from Mercury and about 100 minutes before its closest approach, when it passed a mere 200 kilometers (124 miles) above Mercury's surface.

In the approach movie, Mercury appears as a sunlit crescent. During the encounter, MESSENGER passed over the night side of the planet, experienced its closest approach with Mercury, and then emerged into daylight. This encounter was the first of three flybys of Mercury planned for the MESSENGER mission.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington


Image 2.2

Click on image to play the movie.

MESSENGER Flies through Mercury’s Magnetosphere

This animation shows a conceptual sketch of Mercury’s magnetosphere at the time of the MESSENGER flyby. The graphs at the bottom show observations made by the Fast Imaging Plasma Spectrometer (FIPS) portion of the Energetic Particle and Plasma Spectrometer (EPPS) instrument as the spacecraft followed the indicated trajectory. The top plot depicts the low-energy plasma of solar wind origin, and the bottom plot shows heavy ion intensities associated with the planet. This flyby was the first survey of the ion plasma of Mercury's space environment. The positions at which the spacecraft first crossed the “bow shock” of the magnetospheric interaction with the solar wind, passed closest approach to the planet, and crossed the outbound bow-shock crossing are indicated.

These results show the expected increases in solar wind plasma density downstream of the bow-shock boundary, as well as significant solar wind plasma densities within Mercury's magnetosphere close to the planet. The latter measurements provide definitive evidence that Mercury's magnetosphere – despite its small size – is not a vacuum but hosts significant densities of heated solar wind plasma. The plasma affects the magnetic field, contributes to the “space weathering” of the planet’s surface, and sputters material from the surface to populate the exosphere. This first detection of heavy pick-up ions, Na+ and other species, near Mercury is consistent with their production by ionization of exospheric neutral species. This complex system and all of its time variations will be studied during the next two MESSENGER flybys as well as throughout the orbital phase of the mission.

Credit: NASA/University of Michigan/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington


Image 2.3

Mercury’s Magnetic field

The plot shows the measured magnitude of the magnetic field of Mercury as MESSENGER executed its first flyby of that planet. MESSENGER’s Magnetometer (MAG) provided definitive identification of all boundaries of the Mercury magnetosphere system, consistent with the observations made with the Fast Imaging Plasma Spectrometer (FIPS) on the Energetic Particle and Plasma Spectrometer (EPPS) instrument, and revealed a much more quiescent system than was seen during the first Mariner 10 flyby. This state of the system was also consistent with the absence of energetic particles as documented by the Energetic Particle Spectrometer (EPS) portion of MESSENGER’s EPPS instrument. Mercury lacks radiations belts similar to the Van Allen belts at the Earth discovered by James Van Allen with a simple particle experiment on Explorer I launched 50 years ago.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/ Carnegie Institution of Washington


Image 2.4

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Mercury’s Internal Magnetic field

This depiction of a simulated Mercury magnetosphere shows representations of the distortions of the planetary magnetic field lines (blue) by the solar wind. Mariner 10 data showed the first evidence for a magnetic field at Mercury, an unexpected result. The equatorial pass of MESSENGER during quiet solar conditions provided better data than were available from Mariner 10.

MESSENGER saw an internal magnetic field that is well described by the field from a dipole nearly aligned with the planet’s spin axis (dipole tilt ~ 10°). This geometry is similar to that observed by Mariner 10 during its first flyby. The field strength is weaker by about one third than that detected by Mariner 10 during its third (and last) flyby, owing primarily to the difference in trajectories (Mariner 10 flow directly over the magnetic pole where the field strength is greatest). When corrected for our best estimate for the external field, the MESSENGER observations and the two Mariner 10 passes are consistent with very similar solutions for the mean planetary magnetic dipole. The dipolar field is consistent with an active electrical dynamo in which the magnetic field is produced by electrical currents flowing in an outer core of molten metal. The observations do not yet allow us to identify whether a small secular variation may have occurred, determine higher order structure in the field, or assess whether crustal magnetic signatures may be present at other longitudes. A combination of the next two flybys and the orbital phase of MESSENGER’s mission will be required to sort out all of these possible effects.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington


Image 2.5

Mercury’s Sodium Tail

This plot shows the intensity of emission of light associated with sodium atoms in the vicinity of Mercury. The observations were made with the Ultraviolet and Visible Spectrometer (UVVS) section of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS). The intensity (up to 40 kiloRayleighs) indicates the relative abundance of material, in this case sodium atoms, along the observational line of sight back to the spacecraft. While sodium from Mercury has been observed with Earth-based telescopes, this is the highest-spatial-resolution image ever made. The geometry and observing circumstances have to be disentangled to infer the true spatial distribution, but the observations do confirm a north-south asymmetry that has previously been observed in ground-based sodium images.

The sodium emission is at 589 nm (in the visible part of the spectrum and the same wavelength, or color, as in sodium lamps and street lights on Earth). Because sodium atoms have intense emission, they are easy to detect, and this makes sodium a good tracer for other volatile elements in Mercury’s exosphere.

Credit: NASA/University of Colorado/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington


Image 2.6

Mercury’s Hydrogen Tail

This plot shows Lyman-alpha emission at 121.6 nm associated with neutral hydrogen in the near vicinity of Mercury. This is the first detection of hydrogen tail emission at Mercury and the first time that neutral hydrogen and sodium atoms have been observed in the tail simultaneously. This emission is about 100 times less intense than the sodium emission. As with the sodium emission, discovering the true spatial distribution requires more analysis. The similar asymmetries in hydrogen, derived from the solar wind, and the much heavier sodium nonetheless suggest that solar-wind interactions with Mercury’s magnetosphere have played a strong role in supplying tail material at the time of MESSENGER’s flyby.

Observing the Lyman alpha emission line, deep in the ultraviolet, is possible only from space. Such hydrogen emissions were also observed by Mariner 10 but only on the subsolar limb.

Calcium was detected in the near-Mercury exosphere by MESSENGER and has also been observed telescopically from Earth. Other species are expected to be seen in Mercury’s exosphere as well, but the orbital phase of the mission offers better opportunities to observe them.

Credit: NASA/University of Colorado/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington


Image 2.7

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Seeking Information on Mercury’s Mineralogy

This plot shows the ground track of observations made by the Visible and Infrared Spectrograph (VIRS) component of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS). The ground track is projected onto a MESSENGER image of the portion of the planet seen in high-resolution by MESSENGER for the first time.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington


Image 2.8


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Mercury Surface Spectra

This plot shows the relative spectral reflectance as a function of wavelength at the two locations indicated on the previous graphic. The visible and infrared portions of the spectra are shown for the two nearby areas, one including ejected material from a bright, relatively young crater and the other from surrounding plains. The two spectra have been shifted vertically to match at 850 nm (in the near-infrared). Differences between the two spectra, most notable in the infrared, are indicative of differences in the mineral abundances in these two regions.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Presenter #3
Maria T. Zuber, MESSENGER Science Team Member
Massachusetts Institute of Technology

Image 3.1

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First Laser Altimetry for Mercury

At top center is the first laser altimeter profile of Mercury’s topography, taken by MESSENGER’s Mercury Laser Altimeter (MLA) instrument during the spacecraft’s flyby of Mercury on January 14, 2008. At bottom center is the MLA ground projected onto a mosaic of radar images obtained by Harmon and others at the Arecibo Observatory in Puerto Rico.

The interval during which MESSENGER was sufficiently close to the planet to be within measurement range of the MLA was when the spacecraft was on the night side, so there are no corresponding images of this region acquired by MESSENGER during this flyby; this region was also unseen by Mariner 10. The length of the profile is about 3200 km (about 2000 miles), and the dynamic range in elevation across the profile is about 5 km (about 3 miles). The profile sampled numerous craters and basins.  The vertical exaggeration in the figure is 105:1.

At top left is a photograph of the MLA flight unit.

Credit: NASA/Goddard Space Flight Center/Cornell University/Johns Hopkins University Applied Physics laboratory/Carnegie Institution of Washington


Image 3.2

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Topographic Close-up

A close-up of the Mercury Laser Altimeter (MLA) profile of Mercury acquired during MESSENGER’s first Mercury flyby on January 14, 2008.  Comparison with an Arecibo radar image mosaic (bottom) provided by Harmon and co-workers shows that the two largest depressions are adjacent impact craters. The craters have rim-to-rim diameters of 107 km (left) and 122 km (right).  The root mean square roughness of the floor the larger crater is ~35 m.  The vertical exaggeration in the figure is 35:1.

Credit: NASA/Goddard Space Flight Center/Cornell University/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Presenter #4
Robert G. Strom, MESSENGER Science Team Member
University of Arizona

Image 4.1

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The Great Caloris Basin on Mercury

This image shows details of the Caloris basin, one of the largest impact basins in the solar system. Caloris was discovered in 1974 from the Mariner 10 images, but when Mariner 10 flew by Mercury, only the eastern half of the basin was in daylight. During its first flyby of Mercury, on January 14, 2008, the MESSENGER spacecraft was able to snap the first high-resolution images of the western half of the basin. This image is a compilation of pictures from the Mariner 10 mission (right portion of the image) and images from MESSENGER's Narrow Angle Camera (NAC), part of the Mercury Dual Imaging System (left portion of the image).

When Mariner 10 imaged the Caloris basin, the lighting conditions were very different from those experienced by MESSENGER, as is evidenced by the visible seam created when images from both missions are mosaicked together. Despite the different lighting conditions, the MESSENGER images show that the Caloris basin is even larger than previously believed. On the basis of images from Mariner 10, the rim of the Caloris structure was estimated at about 1300 km (about 800 miles) in diameter, shown as a yellow dotted line in this image. MESSENGER's images, which allow the entire Caloris basin to be seen at high-resolution for the first time, indicate that the basin rim, shown as a blue dotted line in the image, is actually closer to 1550 kilometers (about 960 miles) in diameter. Understanding the formation of this giant basin will provide insight into the early history of major impacts in the inner Solar System, with implications not just for Mercury, but for all the planets, including Earth.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington/Brown University


Image 4.2

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Double Ring Crater

This scene was imaged by MESSENGER’s Narrow Angle Camera (NAC) on the Mercury Dual Imaging System (MDIS) during the spacecraft’s flyby of Mercury on January 14, 2008. The scene is part of a mosaic that covers a portion of the hemisphere not viewed by Mariner 10 during any of its three flybys (1974-1975). The surface of Mercury is revealed at a resolution of about 250 meters/pixel (about 820 feet/pixel). For this image, the Sun is illuminating the scene from the top and north is to the left.

The outer diameter of the large double ring crater at the center of the scene is about 260 km (about 160 miles). The crater appears to be filled with smooth plains material that may be volcanic in nature. Multiple chains of smaller secondary craters are also seen extending radially outward from the double ring crater. Double or multiple rings form in craters with very large diameters, often referred to as impact basins. On Mercury, double ring basins begin to form when the crater diameter exceeds about 200 km (about 125 miles); at such an onset diameter the inner rings are typically low, partial, or discontinuous. The transition diameter at which craters begin to form rings is not the same on all bodies and, although it depends primarily on the surface gravity of the planet or moon, the transition diameter can also reveal important information about the physical characteristics of surface materials. Studying impact craters, such as this one, in the more than 1200 images returned from this flyby will provide clues to the physical properties of Mercury’s surface and its geological history.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

 

Presenter #5
Louise Prockter, Instrument Scientist for the Mercury Dual Imaging System
The Johns Hopkins University Applied Physics Laboratory

Image 5.1 - 5.5

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MESSENGER Timeline M1 V0
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Mercury’s Violent History

This image of Mercury’s surface was acquired during MESSENGER’s first flyby of the planet on January 14, 2008, through the lens of the Narrow Angle Camera (NAC), part of the Mercury Dual Imaging System (MDIS). The image was acquired when MDIS was 11,588 km (7,200 miles) from Mercury’s surface.

Several processes have acted to sculpt Mercury’s surface over time, and evidence of them is abundant in this image. This scene shows at least five different events in Mercury’s surface history. The large crater to the lower left of the image measures ~230 km (143 miles) in diameter and has a prominent crater, about 85 km (53 miles) across, nestled inside it, south of its center. Both of these craters were subsequently filled with a material that appears to have been emplaced in a relatively fluid form, as evidenced by the fact that the material “embays” or onlaps the ejecta blanket surrounding the rim of the smaller crater. The larger crater is filled almost to its rim with this smooth plains material, which is thought to be of volcanic origin. Subsequent to the plains emplacement was the formation of the linear feature trending southwest to northeast across the lower half of the scene. This feature is a lobate scarp, similar to many others found on Mercury’s surface, and thought to originate when compressional stresses crumpled the surface. The last major episode in the history of this region is the impact that formed the large crater at the top of the image. The formation of this crater resulted in impact-derived material, known as ejecta, being thrown out radially for large distances. Some of this ejecta formed chains of “secondary” craters as it impacted back onto the surface; some of these secondary craters are visible atop the lobate scarp.

By careful examination of the relationships among features within images such as these, Mercury’s surface history can be teased out, enabling us to better understand the evolution of this planet and other terrestrial worlds.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington


Image 5.6

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“The Spider” – Radial Troughs within Caloris

The Narrow Angle Camera of the Mercury Dual Imaging System (MDIS) on the MESSENGER spacecraft obtained high-resolution images of the floor of the Caloris basin on January 14, 2008. Near the center of the basin, an area unseen by Mariner 10, this remarkable feature – nicknamed “the spider” by the science team – was revealed. A set of troughs radiates outward in a geometry unlike anything seen by Mariner 10. The radial troughs are interpreted to be the result of extension (breaking apart) of the floor materials that filled the Caloris basin after its formation. Other troughs near the center form a polygonal pattern. This type of polygonal pattern of troughs is also seen along the interior margin of the Caloris basin. An impact crater about 40 km (~25 miles) in diameter appears to be centered on “the spider.” The straight-line segments of the crater walls may have been influenced by preexisting extensional troughs, but some of the troughs may have formed at the time that the crater was excavated.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington


Image 5.7

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Mercury Shows Its True Colors

MESSENGER's Wide Angle Camera (WAC), part of the Mercury Dual Imaging System (MDIS), is equipped with 11 narrow-band color filters. As the spacecraft receded from Mercury after making its closest approach on January 14, 2008, the WAC recorded a 3x3 mosaic covering part of the planet not previous seen by spacecraft. The color image shown above was generated by combining the mosaics taken through the WAC filters that transmit light at wavelengths of 1000 nanometers (infrared), 700 nanometers (far red), and 430 nanometers (violet).  These three images were placed in the red, green, and blue channels, respectively, to create the visualization presented here.  The human eye is sensitive only across the wavelength range from about 400 to 700 nanometers.  Creating a false-color image in this way accentuates color differences on Mercury's surface that cannot be seen in black-and-white (single-color) images.

Color differences on Mercury are subtle, but they reveal important information about the nature of the planet's surface material. A number of bright spots with a bluish tinge are visible in this image. These are relatively recent impact craters. Some of the bright craters have bright streaks (called "rays" by planetary scientists) emanating from them. Bright features such as these are caused by the presence of freshly crushed rock material that was excavated and deposited during the highly energetic collision of a meteoroid with Mercury to form an impact crater. The large circular light-colored area in the upper right of the image is the interior of the Caloris basin. Mariner 10 viewed only the eastern (right) portion of this enormous impact basin, under lighting conditions that emphasized shadows and elevation differences rather than brightness and color differences. MESSENGER has revealed that Caloris is filled with smooth plains that are brighter than the surrounding terrain, hinting at a compositional contrast between these geologic units. The interior of Caloris also harbors several unusual dark-rimmed craters, which are visible in this image. The MESSENGER science team is working with the 11-color images in order to gain a better understanding of what minerals are present in these rocks of Mercury's crust.

The diameter of Mercury is about 4880 kilometers (3030 miles). The image spatial resolution is about 2.5 kilometers per pixel (1.6 miles/pixel. The WAC departure mosaic sequence was executed by the spacecraft from approximately 19:45 to 19:56 UTC on January 14, 2008, when the spacecraft was moving from a distance of roughly 12,800 to 16,700 km (7954 to 10377 miles) from the surface of Mercury.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington


Image 5.8

Click on image to to play the movie.

MESSENGER Departs Mercury

As MESSENGER completed its successful flyby of Mercury, the Narrow Angle Camera (NAC), part of the Mercury Dual Imaging System (MDIS), took images of the planet as the spacecraft departed. Beginning on January 14, 2008, about 100 minutes after MESSENGER's closest pass by the surface of Mercury, until January 15, 2008, about 19 hours later, the NAC acquired one image every four minutes. In total, 288 images were snapped during this time and were compiled sequentially to produce this movie. At the start of the movie, MESSENGER is about 34,000 kilometers (about 21,000 miles) from Mercury, and the first image has a field of view of about 950 kilometers (about 590 miles) in width. At the end of the movie, the MESSENGER spacecraft is a distance of about 440,000 kilometers (270,000 miles) from Mercury.

This movie shows the end of MESSENGER's first encounter with Mercury. MESSENGER will fly by Mercury two additional times during the mission, in October 2008 and September 2009. In March 2011, MESSENGER will enter into an orbit around Mercury and begin a year-long scientific investigation of the planet.

Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

 

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