Biology
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p13a1251r&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P13A-1251
Biology
[5220] Planetary Sciences: Astrobiology / Hydrothermal Systems And Weathering On Other Planets, [5464] Planetary Sciences: Solid Surface Planets / Remote Sensing, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The Mars Exploration Rover (MER) Spirit has discovered deposits of bright yellowish and whitish soils that have been confirmed by Spirit’s Alpha Particle X-Ray Spectrometer (APXS), Mössbauer spectrometer, and Miniature Thermal Emission Spectrometer (Mini-TES) instruments to contain ferric sulfates and/or opaline silica. These deposits have important implications for the history of water at Gusev Crater, as they have been interpreted by Squyres et al. (2008, Science, 316, 738) to have formed in a hydrothermal environment. Repeated Pancam 11 color visible to short-wave near-IR observations have been made at the Tyrone, Kit Carson and Ulysess soil exposures, and changes in Vis-NIR spectra and/or soil texture and morphology have been observed at all three sites. We have identified at least three possible explanations for the observed changes: 1) dust deposition; 2) aeolian sorting; and/or 3) a mineralogic change after exposure to martian surface conditions. To better characterize how and why these soils are changing with time, we present a detailed multispectral analysis of the seven Pancam image sequences at Tyrone, the two at Kit Carson, and the nine at Ulysses that have been acquired as of sol 2000 (August 18, 2009). At the Tyrone “yellow” soil, the blue-to-red (432 to 753 nm) spectral slope decreased after roughly 175 sols of exposure to the martian surface, as described by Wang et al. (2008, JGR, 114, 461). This spectral change is contrary to the “reddening” that would be expected from dust deposition, but could be consistent with dehydration pathways of certain ferric sulfates, such as from copiapite to amorphous ferric sulfates or to rhomboclase (Wang et al., 2008, AGU). The Tyrone “yellow” soil also exhibits increased 535 nm and 803 nm band depths with time, which is further suggestive of a mineralogic change. Pancam spectra of Kit Carson appear to have changed similarly to those of Tyrone, with 535 nm and 864 nm absorptions developing after four sols of exposure; these results are preliminary, however, as the image sequences require additional calibration. At Ulysses, any spectral variations with time are subtler, but significant morphologic and textural changes have occurred. We have observed slumping within the wheel trench, movement of individual granules, disappearance of fines, and disintegration of soil clods at both Ulysses and Kit Carson (any such changes at Tyrone, which was imaged from a distance of tens of meters, could not be resolved). Determining whether these changes result solely from aeolian sorting or in part from desiccation during a mineralogic change is a major goal of our continuing analysis.
Arvidson Ray E.
Bell Jon F.
Johnson Jay Robert
Rice Melissa S.
Wang Anzhong
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