HR: 14:00h
AN: P13B-02    [Abstracts]
TI: High-Resolution Textures of Soils and Rocks at Gusev Crater and Meridiani Planum From the Mars Exploration Rover Microscopic Imagers
AU: * Herkenhoff, K E
EM: kherkenhoff@usgs.gov
AF: USGS Astrogeology Team, 2255 N. Gemini Dr., Flagstaff, AZ 86001 United States
AB: The Microscopic Imagers on the Spirit and Opportunity rovers have returned images of Mars with higher resolution than any previous camera system, allowing detailed petrographic and sedimentological studies of the rocks and soils at the Gusev and Meridiani landing sites. The Microscopic Imager (MI) is a fixed-focus camera mounted on the robotic arm of each Mars Exploration Rover (MER). The MI was designed to function like a geologist's hand lens, acquiring images at a scale of 31 microns/pixel over a broad spectral range (400-700 nm). The MI provides critical documentation of the constitution and texture of targets analyzed by the other MER in-situ instruments. The MI on the Spirit rover found weakly bound agglomerates of dust in the soil near the Columbia Memorial Station. Bedforms have coarser particles at their crests and finer grains in the troughs, like eolian ripples on Earth. Some of the brushed or abraded rock surfaces show igneous textures and evidence for alteration rinds, coatings, and veins consistent with secondary mineralization. The textures of rocks on the floor of Gusev crater are consistent with a volcanic origin and subsequent alteration and/or weathering by impact events, wind and possibly water. MI observations in the ''Columbia Hills'' are consistent with interpretations, based on syntheses of various MER data, that the rocks there are more altered than those on the floor of Gusev. The MI on the Opportunity rover has returned images of the Meridiani landing site that include evidence for both surface and ground water activity in Mars' ancient past. Soil particles imaged by the MI show constituents typical of windblown materials. The uppermost millimeter of some soils is weakly cemented, probably by salts precipitated from evaporating brines. Rock outcrops are laminated on a millimeter scale; image mosaics of cross-stratification suggest that some sediments were deposited by flowing water. Vugs in some outcrop faces are probably molds formed by dissolution of relatively soluble minerals during diagenesis. MI data support the hypothesis that hematite-rich spherules (typically 3-5 mm diameter) observed in outcrops and soils also formed diagenetically as concretions.
DE: 5470 Surface materials and properties
DE: 6225 Mars
DE: 6297 Instruments and techniques
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting