Mathematics – Logic
Scientific paper
May 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusm.u43a..03g&link_type=abstract
American Geophysical Union, Spring Meeting 2004, abstract #U43A-03
Mathematics
Logic
5415 Erosion And Weathering, 5464 Remote Sensing, 5470 Surface Materials And Properties, 5480 Volcanism (8450), 5499 General Or Miscellaneous
Scientific paper
The Mars Exploration Rover Spirit (MER-A) landed within the 160 km diameter Gusev crater (14.5692S, 175.4729E) on January 3rd, 2004. Landing occurred on a generally flat plain characterized by small, shallow depressions (referred to as hollows) and poorly defined ridges with only a few meters relief. Low hills and the rim of a 200 meter diameter crater (nick-named Bonneville) mark the horizon to the east-southeast and northeast, respectively. Gravel to cobble sized rocks cover 5% of the local surface and there are relatively few boulders. Surface albedo is 0.19, the lowest observed within the predicted landing ellipse, and is thought to reflect removal of fines during dust devil passage. Much of the surface is dominated by sand and silt and finer sized particles comprising soils and local drift deposits. Rocks are noticeably smaller than at previous Mars landing sites and display a broad range in size and angularity. Some are faceted and likely reflect wind erosion, whereas others are pitted and may possess vesicles. Fractured and fragmented rocks are more abundant than at previous landing sites. Most rocks are either embedded in the substrate or perched on the surface and the vast majority are dark in color. Variable dust covering likely accounts for the appearance of lighter rocks and all observed so far are compositionally consistent with olivine basalts. Relatively high albedo soils possess a honeycomb texture characterized by rare discrete grains and elevated sulphur and chlorine abundance. A few soil grains appear tabular, but most are unresolvable fines. Soils retain texture after placement of the Mossbauer instrument, thereby indicating some strength and are consistent with the presence of an orthochemical cement. Local eolian drifts occur as fines partially filling local hollows and as numerous accumulations generally in the lee of obstacles. By contrast, surfaces adjacent to some hollows possess abundant perched rocks and appear deflated. Examination of the grains comprising the coarser drift deposits reveals a bi-modal distribution of fine and coarse sand sizes with the coarse grains being rounded, sometimes oblate, and concentrated along the crests of the drifts. Grains also occur as small fillets at the base of some rocks and indicate sufficient strength to withstand saltation transport. Collectively, these properties indicate local bed forms are ripples, not dunes. Observations of the landing site to date reveal a surface dominated most recently by eolian, impact, and perhaps volcanic processes. While conclusive evidence for ancient water-lain deposits remains elusive, the action of these more recent processes may mask their signature. In an attempt to deconvolve the broader geologic history, the Spirit rover is traversing 250 meters to access the rim of crater Bonneville. A radial traverse across the Bonneville ejecta and view of any crater wall stratigraphy and interior deposits should lead to a better understanding of the full suite of processes that have operated in Gusev crater over geologic time.
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