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MESSENGER Telecon Multimedia Page

Presenter #1
Marilyn M. Lindstrom, MESSENGER Program Scientist
NASA Headquarters, Washington

Image 1.1

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 previously seen by spacecraft.

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Presenter #2
Daniel J. O'Shaughnessy
The Johns Hopkins University Applied Physics Laboratory

Image 2.1

MESSENGER's interplanetary trajectory includes six planetary flybys and six large bi-propellant burns to achieve Mercury orbit in 2011. MESSENGER is about to complete the leg of the trajectory between the first and second Mercury flybys. This leg also included Deep-Space Maneuver 3 (DSM-3), a 72.5 meters per second bi-propellant maneuver executed on March 19, 2008 to target the second Mercury flyby at an altitude of 200 kilometers.

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Image 2.2

Solar radiation (sunlight) exerts a small force on MESSENGER at all times. Changing the spacecraft attitude and solar array configuration with respect to the Sun alters the direction of the reflected photons and the resultant force due to solar radiation pressure. MESSENGER uses attitude and solar array manipulation to apply this force to steer the spacecraft and reduce the flyby targeting error. This "solar sailing" conserves propellant and reduces mission risk by eliminating the flyby targeting maneuvers and increases flyby targeting accuracy

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Image 2.3

Because the gravity assist from the flyby is critical, deviation from the targeted flyby point can result in an irrecoverable trajectory change. Deep-Space Maneuver 3 in December 2007 was executed as planned, but the maneuver error still required correction to avoid using more then half of the mission reserve propellant (~80 meters per second), shown as the red "+" in the figure. Normally, this correction is accomplished with a series of small maneuvers within two to three months of the flyby to walk progressively closer to the target, where each maneuver cleans up the errors in the previous burn; MESSEGNER opted for a more novel approach by using solar sailing. MESSENGER was successfully able to navigate to within 1 kilometer of the targeted flyby point without consuming a single drop of propellant in more than six months! MESSENGER is the first interplanetary mission to demonstrate the utility of solar sailing for precision targeting at a planetary flyby.

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Presenter #3
Scott L. Murchie
The Johns Hopkins University Applied Physics Laboratory

Image 3.1

This mosaic of Mercury, taken by Mariner 10 as it approached the planet for its first flyby on March 29, 1974, covers about half of the face of Mercury that will be illuminated by the Sun on MESSENGER's second flyby of the planet on October 6, 2008. The shadowed area of the surface to the right of the Mariner 10 mosaic is territory that will be imaged from a spacecraft for the first time by MESSENGER.

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Image 3.2

This map of Mercury compares existing imaging coverage of Mercury with the new coverage that will be obtained by MESSENGER. The images obtained by Mariner 10 are shown in the eastern half of the map. The same part of Mercury was illuminated by the Sun during all three of its flybys, and the wedge-shaped gap was beyond the planet's limb from the spacecraft's perspective and blocked from direct view. New coverage obtained during MESSENGER's first flyby on January 14, 2008, is shown outlined in white. The coverage to be obtained during the second flyby on October 6, 2008, is shaded purple and will fill in most of the previously un-imaged areas.

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Image 3.3

Most of MESSENGER's imaging coverage of Mercury during the second flyby on October 6, 2008, will be taken as a series of mosaics. Two inbound mosaics showing a crescent Mercury and seven outbound mosaics showing a gibbous Mercury will provide 629 images used to map the planet. In addition 64 images will be taken for optical navigation, and 197 images will be taken as part of a departure movie as MESSENGER recedes from the planet. Another 398 images will be taken for various instrument calibrations whose results will be used to refine processing of the data. In this view, an airbrush map constructed from Mariner 10 images has been draped over the part of the planet that will be visible to MESSENGER about 40 minutes after closest approach on the night side of the planet. The blue outlines show the images comprising the first two departure mosaics, which will have resolutions of 100 to 300 meters per pixel.

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Image 3.4

In this view, an airbrush map constructed from Mariner 10 images has been draped over the part of Mercury that will be visible to MESSENGER about 75 minutes after closest approach on the night side of the planet. The blue outlines show the images comprising the fifth departure mosaic, which will have a resolution near 500 meters per pixel.

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Image 3.5

The images that MESSENGER obtains during its second flyby will be used to investigate key questions about the geology of Mercury. This enhanced color mosaic of the region surrounding the Caloris impact basin illustrates two of those questions. The light-toned, buff-colored region to the upper right consists of volcanic plains that infill the interior of Caloris. New images from the second flyby, combined with those from Mariner 10 and MESSENGER's first flyby, will allow the first estimate of what fraction of Mercury's surface is covered by volcanic lava flows. The dark craters within those light plains are thought to be a different rock type excavated from several kilometers depth. The coming flyby will also allow the first near-global survey of where these dark materials are found, and what they may be revealing about the structure of Mercury's crust. The image mosaic was constructed using images taken during MESSENGER's first flyby through violet and two infrared filters.

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Image 3.6

These four images acquired during MESSENGER's first flyby illustrate the kinds of geologic features that the science team will be looking for in images from the second flyby. These features can tell us the types of rocks that make up Mercury's crust and how they were modified by volcanism, deformation, and impact cratering. The upper left image shows a cluster of several volcanic structures at the southwestern edge of Caloris basin. Their irregular, rimless craters are all surrounded by diffuse, brighter, redder material interpreted as pyroclastic volcanic deposits. The occurrence of additional volcanoes will help clarify how the style of Mercury's volcanism varied over the planet. The largest of the volcanic craters is approximately 25 kilometers across. The upper right image shows the 125-kilometer diameter crater Eminescu. Bright material forming the central peak ring of the crater is spectrally distinctive and its origin is uncertain. New images will help to clarify the spatial distribution and depths of rock units like this one. The lower left image shows a complex of extensional tectonic troughs forming Pantheon Fossae. It is one of only two regions of extensional tectonism and the mission's scientists are anxious to see if more are revealed in the new images. The lower right image shows one of the ridges that are products of horizontal shortening and are prevalent on Mercury. They are best seen at a low Sun angle, available within about 30 degrees of the terminator. The second flyby will cover additional territory under the illumination conditions well-suited to detect and map tectonic features, including previously unseen territory as well as regions imaged by Mariner 10 only at high Sun angles. Measurements of the lengths and heights of these ridges provide estimates for the contraction of Mercury's crust, an important measure of the cooling of the planet's interior.

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

Image 4.1

Our information on the geometry of Mercury's planetary magnetic field comes from two flybys of that planet by Mariner 10 in 1974-1975 as well as the first MESSENGER flyby in January of this year. All of those flybys passed close to Mercury's eastern hemisphere (longitudes 0° to 180° east), as the spacecraft ground tracks show on the figure above. MESSENGER's second flyby will provide the first sampling of Mercury's magnetic field over the planet's western hemisphere. The degree of symmetry of the field about the planetary rotation axis will provide important information on the source of the magnetic field, specifically the nature of the magnetic dynamo in Mercury's fluid outer core that gives rise to the global field.

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Image 4.2

MESSENGER's first flyby of Mercury featured the first determination of topography on the innermost planet from a spacecraft laser altimeter. The profile obtained by MESSENGER's Mercury Laser Altimeter (MLA) was on the nightside, over a portion of the planet never viewed by spacecraft cameras, so it was not possible to make a detailed comparison between features on the altimetric profile and features in high-resolution images of the surface. During MESSENGER's second flyby, the Mercury Dual Imaging System (MDIS) will obtain images of most of the region of the first altimetric profile, and MLA will obtain a second profile of topography. All of the region crossed by that second profile has been imaged, either in January by MDIS or earlier by Mariner 10. Detailed comparisons of features in the topographic profiles and in the images will therefore be possible for the first time for both altimeter tracks, and we can expect to learn new information about impact craters, faults, and other geological landforms on Mercury as a result.

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Image 4.3

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) will observe an equatorial strip across the western hemisphere of Mercury during MESSENGER's second flyby. The Visible and Infrared Spectrograph (VIRS) component of MASCS will acquire over 400 spectra (350-1450 nm wavelength) of the surface, including co-aligned observations with the Mercury Laser Altimeter (MLA), color imaging by the Mercury Dual Imaging System (MDIS), and spectral observations in the middle ultraviolet (220-330 nm, with UVVS, the Ultraviolet and Visible Spectrometer component of MASCS). UVVS will also attempt a far-ultraviolet surface spectral reflectance observation (115-170 nm) of the day-lit Mercury surface (not shown on this graphic). The background image is from Mariner 10.

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Image 4.4

The Mercury Atmospheric and Surface Composition Spectrometer (MASCS) instrument will begin a "tail sweep" observation of Mercury's comet-like tail almost 10 hours before closest approach to Mercury. The spacecraft will pivot "up and down," sweeping the field of view of the Ultraviolet and Visible Spectrometer (UVVS) component of MASCS through the extended tail of atoms blown from Mercury's exosphere by the solar wind. For almost 7 hours, UVVS will map Mercury's extended sodium tail, which has been observed telescopically from Earth and by MASCS during MESSENGER's first Mercury flyby. For the second flyby, observations will begin around 100,000 km "downwind" of Mercury, more than twice the distance at which observations began for the first flyby. At about 3 hours from closest approach, UVVS will switch modes to observe calcium and magnesium as well as sodium. While calcium was detected during the first flyby, this is MESSENGER's first attempt to detect magnesium, an expected component of the exosphere but one that has not been seen in Earth-based observations. Mg, Ca, Na, and Hydrogen will be observed during the last segment of the tail sweep and as the spacecraft reorients itself for surface observations and imaging. Following the surface observations, which include altimetry profiles (Mercury Laser Altimeter), high-resolution and color imaging (Mercury Dual Imaging System), and surface spectroscopy from ultraviolet through infrared wavelengths (MASCS), UVVS will concentrate observations on low-altitude hydrogen and mid-altitude hydrogen and sodium gases in Mercury's dayside exosphere.

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