Other
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusm.u23a..08b&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #U23A-08
Other
5400 Planetary Sciences: Solid Surface Planets, 5464 Remote Sensing, 5470 Surface Materials And Properties, 6235 Mercury
Scientific paper
The January 2008 flyby of Mercury by the MESSENGER spacecraft provided the first close-up images of the planet since the Mariner 10 observations of 1974-75. MESSENGER's Mercury Dual Imaging System (MDIS) collected high signal-to-noise-ratio images with two cameras: a high-spatial-resolution broadband visible Narrow Angle Camera (NAC), and a lower-spatial- resolution multispectral Wide Angle Camera (WAC). The WAC has 11 narrow-band color filters with center wavelengths in the range 430 to 1020 nm. A spot spectrometer, the Visible and Infrared Spectrograph (VIRS) component of the Mercury Atmospheric and Surface Composition Spectrometer (MASCS), collected spectra over the range 350 to 1450 nm. The MESSENGER observations cover portions of the planet seen by Mariner 10, as well as new regions not previously imaged by spacecraft. Studies of the Moon over the past forty years — via spectral analysis of returned lunar samples, Earth-based telescopic reflectance spectra, and imaging by the Galileo and Clementine spacecraft, along with theoretical work on the interaction of light with a silicate regolith — provide a framework for interpreting spectra of Mercury. Ferrous iron in silicate minerals (primarily pyroxene and olivine) and glasses has a strong influence on lunar reflectance spectra, producing diagnostic absorption features. "Space weathering," the response of a regolith to micrometeorite bombardment and solar-wind sputtering, tends to reduce the contrast of absorption bands and introduces an overall strong positive ("red") slope to the spectrum. These spectral effects are attributed to tiny metallic iron particles created by vapor deposition during space weathering. Spectrally neutral opaque phases are dark with a flat "bluish" spectral slope and lack strong absorptions. Ilmenite, an iron-titanium oxide, is the key opaque phase in lunar samples. The MESSENGER multispectral observations validate and greatly extend the knowledge gained from analysis of Mariner 10 two-color data. Major color and albedo units on the portion of Mercury covered by MDIS include: (1) plains that have albedo slightly greater than average Mercury located within the Caloris basin and filling other large craters, (2) dark, relatively blue material surrounding the Caloris and Tolstoj basins and in a large region southwest of Caloris, (3) intermediate albedo material in the equatorial region. Minor units include very bright material in some crater floors and very reddish deposits found on the margins of Caloris. On a global scale, Mercury's surface appears to have a limited range of ferrous iron content, much smaller than the range found on the Moon. Spectral trends consistent with the effects of space weathering are present and suggest that the surface of Mercury experiences more intense space weathering than does the Moon. There is also evidence that variation in opaque content is a major controller of the color of Mercury.
Blewett Dave T.
Denevi Brett Wilcox
Domingue Donovan L.
Gillis-Davis Jeffery J.
Head James W.
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