HR: 0800h
AN: P11A-0254    [Abstracts]
TI: Wind-Driven Particle Mobility on Mars: Insights from MER Observations
AU: * Sullivan, R
EM: rjs33@cornell.edu
AF: Cornell University, CRSR/Astronomy, Ithaca, NY 14853,
AU: Arvidson, R
AF: Washington University, Dept. Earth & Planet. Sci., St. Louis, MO 63130,
AU: Bell, J F
AF: Cornell University, CRSR/Astronomy, Ithaca, NY 14853,
AU: Geissler, P
AF: USGS, 2255 N. Gemini Drive, Flagstaff, AZ 86001,
AU: Golombek, M
AF: JPL, 4800 Oak Grove Drive, Pasadena, CA 91109,
AU: Greeley, R
AF: ASU, School of Earth and Space Exploration, Tempe, AZ 85287-1404,
AU: Herkenhoff, K
AF: USGS, 2255 N. Gemini Drive, Flagstaff, AZ 86001,
AU: Johnson, J
AF: USGS, 2255 N. Gemini Drive, Flagstaff, AZ 86001,
AU: Thompson, S
AF: U. Nevada-Reno, Geol. Sciences, Reno, NV 89557,
AU: Whelley, P
AF: SUNY-Buffalo, Dept. Geol., Buffalo, NY 14260-3050,
AB: High-resolution images from MOC and HiRISE reveal numerous small, linear, light-toned bedforms in settings all across Mars. These features represent one of the most abundant aeolian feature types on the planet, yet their nature and origin remain uncertain. Larger, dark-toned features have been identified confidently as dunes from their morphologies; they presumably are relatively depleted of dust and some therefore could be currently active, but only minor surface changes to a small number of dunes have been reported. There have been no reports of changes to any of the numerous light-toned bedforms. It is problematic that winds responsible for frequently raising dust do not seem to significantly affect bedforms that very likely are composed of (more easily-entrained) sand-sized particles. Here we consider factors other than wind frequency that control bedform mobility across Mars, applying observations from MER traverses at Gusev and Meridiani Planum. (1) MI images show that surface dust at Gusev (and likely elsewhere across Mars) typically occurs as extended, fragile aggregates that should be far easier to entrain than mono-particle "dust"-sized grains. (2) Light-toned bedforms investigated at Gusev are coarse-grained ripples (i.e., bedforms with coarse grains mantling finer-grained, sandy interiors). Currently they are crusted and dust-covered. We suggest that the numerous small, linear, light-toned bedforms seen in high resolution orbital images are coarse-grained ripples also. Although such ripples are much less familiar on Earth compared with ripples and dunes having unimodal particle size-frequencies, we suggest this is partly due to the lack of free quartz on Mars available for contributing to an abundant, durable, very well-sorted sediment supply for saltation. Poorly-sorted debris is organized by wind into relatively slow-moving coarse- grained ripples, so in the absence of quartz, we speculate that coarse-grained ripples should be relatively more common on Mars than on Earth. The relatively slow rate of movement typical of coarse-grained ripples makes these features more vulnerable to immobilization by induration developing during extended periods of quiescence. (3) Spirit also visited a darker-toned unit ("El Dorado") potentially analogous to many similar dark features observed from orbit that have been interpreted as aeolian deposits. Spirit found very slightly crusted (nearly cohesionless), mafic, 200-300 micron sand overlying unconsolidated finer mafic sand. Induration within the dark-toned unit cannot proceed far between disruptions by frequent wind events strong enough to initiate movement of the fine-medium sand. (4) The same fine-medium sand composing El Dorado also is found in small, widely-scattered drifts and in scattered patches of small ripples. Perceptible crest migration of ripples composed of these grains occurred when high winds affected Spirit's site during recent global dust storm activity. (5) At Meridiani Planum, strong wind events associated with the same global dust storm activity--very likely the strongest wind events ever experienced by Opportunity--mobilized 100 micron mafic sand and a few coarser particles (in creep), but only within areas disturbed by the rover wheels. Most changes involved stripping of 100 micron sand from tracks where original cohesive induration of the surface had been destroyed by remolding under wheel movement.
DE: 5415 Erosion and weathering
DE: 5460 Physical properties of materials
DE: 5470 Surface materials and properties
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2007 Fall Meeting