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K. E. Herkenhoff (U. S. Geological Survey), Athena Science Team
The Athena science payload on the Mars Exploration Rovers (MER) includes the Microscopic Imager (MI). Initial results of the MI experiment on both MER rovers (Spirit and Opportunity) have been published previously. Highlights of these and more recent results are described below and will be presented at the meeting.
Spirit MI observations of soil surfaces in Gusev Crater are consistent with electrostatic cohesion or minor cementation of dust grains. Bedforms at Gusev have coarser particles at their crests and finer grains in the troughs, like aeolian ripples on Earth. MI observations of RAT holes in rocks of the Columbia Hills show poorly sorted, subangular to subrounded clasts of sizes ranging down to the MI resolution limit. These images, along with observations by the other Athena instruments, suggest that these rocks are altered volcaniclastics or impact ejecta. The investigation of these rocks continues as Spirit climbs higher into the Columbia Hills.
Opportunity MI observations of soil-like materials within Eagle crater and on the surrounding Meridiani plains suggest that cementation of surface particles has formed a crust, perhaps caused by precipitation of various salts that bridge soil particles. MI images indicate that outcrop rocks have four principal components. MI images document spatial relationships among these constituents, recording a complex history of deposition and diagenesis. Sandy laminae have been cemented, probably by sulfate minerals, during earliest diagenesis. The large vugs cut across bedding, indicating that the minerals that once filled them also formed diagenetically within the sediments. MI images and mosaics of outcrops provide evidence for the presence of small-scale cross bedding with festoon geometry at Meridiani Planum. The MI images confirm two key features that lead to the interpretation of water having flowed at times across the surface at the landing site: centimeter-scale cross-stratification and festoon geometry of cross-lamination.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.