Mathematics – Logic
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p21b..04s&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P21B-04
Mathematics
Logic
5415 Erosion And Weathering, 5470 Surface Materials And Properties
Scientific paper
Previous telescopic, orbital, and in situ exploration has shown the significance of aeolian processes on Mars. The twin MER vehicles have examined the effects of aeolian processes along geological traverses at two Mars landing sites. "Spirit" landed on a dust devil track on plains within Gusev crater, and encountered scattered low bedforms and ventifacts along its traverse to the Columbia Hills. Particle size-frequency variations between bedform crests and troughs are consistent with terrestrial ripple characteristics. Wheel disturbances in one bedform revealed the presence of a dust-covered coarse sand monolayer surface crust overlying a finer-grained, less sorted interior. Several lines of evidence are consistent with NW winds affecting the plains in this part of Gusev crater: (1) slightly asymmetric ripples sparsely distributed across the plains are oriented NNE/SSW and have slightly steeper ESE faces that are also dustier (as determined from albedo and thermal IR spectroscopy); (2) facets, flutes, and grooves on rocks interpreted as ventifacts are most abundant on NW exposures; and (3) asymmetric debris piles from Rock Abrasion Tool grinding extend to the SE. This evidence is consistent with afternoon WNW winds predicted in the area by mesoscale climate models. No dust devils have been observed yet (through 240 sols) by "Spirit." The landing site for "Opportunity" on the plains of Meridiani Planum was less dusty than the Gusev site. Hematite-enriched aeolian ripples dominate the plains, and contribute to the hematite signature detected by MGS TES. Trenching one of these bedforms revealed a surface crust of hematite-enriched spherule concretion fragments, and a substantial fraction of very fine sand in the ripple interior. Very fine sand is also found on the relatively flat areas between ripples, along with spherules and partly buried spherule fragments. Individual plains ripples are oriented about N26E but commonly are grouped en echelon into alignments along a secondary orientation of about N4E, suggesting reorientation during a clockwise change in wind direction. With a few exceptions, bedforms found inside depressions are different from ripples on the plains. A patch of ripples composed of dark, very fine sand on the floor of Eagle crater had lower abundance of finer-grained materials seen in soils elsewhere within Eagle. These ripples are oriented about N38E, consistent with transverse motion driven by the same winds responsible for the bright wind streak extending S45E downwind from Eagle crater; probably these sands are active. A complex of coalesced star dunes, ripples, and drifts about 50 m across was observed at the bottom of Endurance crater. The bright wind streak extending from Eagle crater is typical of many similar features observed from orbit on the plains of Meridiani Planum. Spectrometer results and morphological observations indicate the bright wind streak primarily is air fall dust remaining in the most protected areas immediately downwind of Eagle crater. In rock outcrops, small tails of sculpted rock extend from some spherules still partially embedded within and protruding from some rock units. These features imply erosion of rock due to saltating particles driven by strong, unidirectional wind episodes with an abundant upwind supply of saltating particles.
Fike David
Golombek Matt
Greeley Ronald
Grotzinger John
Jerolmack Douglas
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