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MESSENGER Teleconference Multimedia Page

Presenter #1
Anthony Carro, MESSENGER Program Executive
NASA Headquarters, Washington, D.C.

Image 1.1
image 1.1

The year 2008 was an eventful one for Mercury science. The MESSENGER spacecraft flew by Mercury twice, first on January 14 and again on October 6, capturing images of previously unseen terrain and increasing spacecraft coverage of Mercury’s surface from 45% to about 90%. These images were taken by the Mercury Dual Imaging System (MDIS) during the two flybys.

Top left (flyby 1): In this enhanced-color image of Mercury, the great Caloris impact basin is the large (1550 km in diameter), circular, orange feature in the center. The contrast between the colors of the basin floor and those of the surrounding plains indicates differences in the composition of surface material in these regions.

Top center (flyby 1): The largest volcano currently identified on Mercury. The irregularly shaped depressions are believed to be volcanic vents, and the bright material with a diffuse outer boundary is believed to consist of deposits erupted form the volcanic vents.

Top right (flyby 1): Unusually elliptical in shape, the crater Sveinsdóttir was produced by the impact of an object that hit Mercury’s surface obliquely. The crater is cut by one of the longest scarps on the planet, Beagle Rupes, which marks the surface expression of a large thrust fault believed to have formed as Mercury cooled and the entire planet contracted. Standard 3-D glasses, with a red filter in front of the left eye and a blue filter in front of the right, can be used to gain a sense of the topography of these features.

Bottom left (flyby 2): A bright crater with an extensive system of rays of impact ejecta. Crater rays tend to fade over time, so this crater is thought to be relatively young.

Bottom middle (flyby 2): An impact basin with a well-developed peak-ring structure interior to the main basin rim. Subsequent impact events produced smaller craters that are superimposed on the larger peak-ring basin.

Bottom right (flyby 2): A view of the interior of the Rembrandt impact basin on Mercury, which has a diameter of roughly 700 kilometers (430 miles). The basin floor has an unusual set of radiating fractures, similar to those found only in the larger Caloris basin.

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

Click on image to enlarge.

Presenter #2
Eric J. Finnegan, MESSENGER Mission Systems Engineer
The Johns Hopkins University Applied Physics Laboratory

Image 2.1

This is a timeline of the core instrument-observing sequence for the third Mercury encounter. Pictured here are the onboard activities of the spacecraft starting 30 hours before and continuing through 30 hours after the closest approach to the planet. Two additional views zoom into the timeline for three hours on either side of the closest approach and zoom further for the period of 50 minutes around the closest approach. This timeline illustrates the comprehensive set of scientific measurements that MESSENGER will capture from Mercury. In all views the size of the planet relative to the distance covered by the time period is displayed. The spacecraft will be traveling from left to right on this timeline, approaching the planet from the night side and departing from the dayside.

Click on image to enlarge.

Image 2.2
image 2.2aimage 2.2a

These sets of images present views of the MESSENGER spacecraft, from the front and back (left image) and from the bottom (right image). The most recognizable feature of the spacecraft, the sunshade, is used to shield the spacecraft from solar radiation as the cruise trajectory and Mercury orbital operations place the spacecraft within 0.3 AU of the Sun. The locations for all seven instrument packages, including their individual instrument sensors, are shown. Note that the thermal blanket material that covers and insulates the spacecraft from cold space has been removed for clarity and viewing of the individual sensors.

Click on image to enlarge.

Presenter #3
Noam R. Izenberg, Mercury Atmospheric and Surface Composition Spectrometer Instrument Scientist
The Johns Hopkins University Applied Physics Laboratory

Image 3.1

This figure displays in map view the path of MESSENGER�s instrument-deck boresight during the dayside observations to be made during the third Mercury flyby. After the "neutron sweep" (dashed red line) is completed, the spacecraft will slew and point 11 times at nine different targets (two observed twice) spanning a range of surface compositions and geological terrains. The Mercury Dual Imaging System (MDIS) wide-angle camera will take images of each target with its 11 color filters. The Visible and Infrared Spectrograph (VIRS) and Ultraviolet and Visible Spectrometer (UVVS) channels of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) will both observe the targets for ~35 seconds each to obtain full spectral coverage from ultraviolet to near-infrared wavelengths (116-1450 nm). VIRS will also obtain visible to near-infrared spectra (300-1450 nm) of areas of the surface between targets.

Click on image to enlarge.

Image 3.2

This slide shows three of the flyby targets. The first is the interior of an older crater 150 kilometers (90 miles) in diameter. The second target is the continuous ejecta blanket of a younger rayed crater 30 km (19 miles) in diameter. The third target is the interior of crater Lermontov, where the deposits have an unusual color suggesting that these materials may have been emplaced by explosive volcanic eruptions. The MASCS spectra will be the first obtained for such deposits on Mercury. The inset shows the full range of the spectra to be acquired at each target.

Click on image to enlarge.

Image 3.3

This slide shows two additional targets that exemplify end-member materials identified during previous flybys on the basis of color and reflectance. A small crater, 35 kilometers (21 miles) in diameter and located inside Homer crater (320 km or 192 miles in diameter), appears to be relatively young and to have excavated subsurface materials that have not yet been subjected to extensive "space weathering." The dark blue portion of the ejecta blanket of Titian crater is an example of "low-reflectance material," characterized by lower reflectance and a shallower or �bluer� slope to its reflectance spectrum than typical for the planet. The inset shows examples of spectral variations expected among different targets to be observed during the flyby.

Click on image to enlarge.

Image 3.4

This movie shows a sped-up representation of the targeted dayside observations during MESSENGER's third Mercury flyby, compressing about 18 minutes and 40 seconds of observations into 38 seconds. The animation begins as MESSENGER's instrument deck boresight crosses the dawn terminator and the Mercury Laser Altimeter (MLA) takes its final ranging observations (shown as pink circles). As MLA turns off, the movie shows the footprints of the Visible and Infrared Spectrograph (VIRS) channel (shown in green) of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) sweeping northward as the spacecraft pivots around its sunward axis. The boresight sweeps northward until it moves off the disk of Mercury, conducting a special observation for the Neutron Spectrometer (NS), with an accompanying exosphere observation by the Ultraviolet and Visible Spectrometer (UVVS) channel of MASCS. The boresight then returns to the surface and tracks to the first of 11 targeted observations on the Mercury dayside. For each targeted observation, the MESSEGNER boresight is set to track a single point on the surface for ~35 seconds, taking a series of full-color images with the Mercury Dual Imaging System (MDIS) wide-angle camera, shown as blue frames in the movie, and a full set of spectra with the VIRS and UVVS channels of MASCS. During this part of the flyby, MDIS and UVVS observe only the targets, while VIRS takes spectra continuously, one every second, as the boresight moves across the surface. A total of nine separate targets are observed, with two revisited twice at different viewing angles. The movie ends as the instrument-deck boresight departs the eastern limb of Mercury to begin dayside exosphere observations by UVVS and, later, global mosaic mapping by MDIS.

Click on image to play the movie.

Presenter #4
Sean C. Solomon, MESSENGER Principal Investigator
Carnegie Institution of Washington, Washington, D.C.

Image 4.1
M3 Coverage

This figure shows the planned imaging coverage for the upcoming encounter. The area of the surface that will be imaged by MESSENGER during Mercury flyby 3, outlined in yellow, includes a portion of Mercury's surface never before seen by spacecraft. Prior to the MESSENGER mission, only 45% of Mercury's surface had been imaged by the Mariner 10. As shown in this figure, with the completion of MESSENGER's three Mercury flybys, nearly all of Mercury's surface will have been viewed at close range by spacecraft, with the exception of the polar regions.

Click on image to enlarge.

Image 4.2

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument will begin a "tail-scan" observation of Mercury's comet-like tail on approach to Mercury, starting more than three times farther from the planet than the similar observations taken during MESSENGER’s second Mercury flyby. During the tail scan, the field of view of the Ultraviolet and Visible Spectrometer (UVVS) channel of MASCS will track along the Sun-Mercury line for 13.5 hours, mapping Mercury's extended sodium tail, which was discovered by telescopic observations from Earth and was mapped by MASCS at close range during MESSENGER's first and second Mercury flyby.

At about 17.5 hours from closest approach, UVVS will switch modes to observe five other species as well as sodium - iron, aluminum, neutral and ionized calcium, and magnesium - and the spacecraft will enter a “tail-sweep” observation mode. During the tail sweep, the spacecraft will pivot "up and down" about the Sun-Mercury line, sweeping through the diffuse tail of atoms pushed out from Mercury's exosphere by solar radiation pressure. Neutral calcium was seen during the first and second Mercury flybys and magnesium was detected for the first time during the second flyby, but this is MESSENGER's first attempt to search for ionized calcium and neutral iron and aluminum. None of these last three species have been seen from Earth, but all are expected to be present.

During this same period, the spacecraft attitude will be modified to permit scans of the exosphere over Mercury’s north and south poles (see inset).  Following observations of the surface by MASCS and other instruments, UVVS will concentrate on observations of hydrogen and sodium in Mercury's dayside exosphere.

Click on image to enlarge.

Image 4.3

This animation shows maneuvers of the MESSENGER spacecraft during a portion of the third Mercury flyby. Several of the maneuvers are designed to improve the capability of MESSENGER’s Neutron Spectrometer (NS) to identify neutron-absorbing elements, most notably iron (Fe) and titanium (Ti), on Mercury’s surface. Thermal neutrons are measured with the Doppler filter effect, which uses the spacecraft velocity (5 km/s) and orientation to identify the slower (2.2 km/s) thermal neutrons. The graph at lower right shows predicted neutron counting rates for three different average surface compositions; blue, green, and red curves denote counting rates for low, medium, and high amounts of Fe and Ti, respectively. The Doppler filter effect reaches its peak neutron enhancement during the spacecraft rotation maneuver at 21:46 UTC. It is at this time that neutrons provide the strongest discriminator of Mercury’s surface composition, as seen by the separation among the three colored curves.

Episodic simulated flashes from MESSENGER's instrument deck during the first half of the animation depict observations by the Ultraviolet and Visible Spectrometer (UVVS) of Mercury's nightside exosphere. The overlapping yellow circles toward the end of the animation represent Mercury Laser Altimeter (MLA) observations of topography. The vertical yellow line at the end of the animation depicts Mercury's dawn terminator, the boundary between night and day.

Click on image to play the movie.


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