Other
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p21c..06h&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P21C-06
Other
[5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties, [5494] Planetary Sciences: Solid Surface Planets / Instruments And Techniques, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
The Athena science payload on the Mars Exploration Rovers (MER) includes the Microscopic Imager (MI), designed to simulate a geologist’s hand lens. The fixed-focus MI is mounted on the instrument arm and can resolve objects 0.1 mm in size or larger. Spirit MI observations of the rocks on “Home Plate” continue to be consistent with a volcaniclastic origin. A total of 124 individual soil samples were analyzed using MI images acquired between landing and Sol 1980, including 28 bedforms, 35 composite soils, 49 unstructured soils, and 6 trenches including natural vertical exposures and those dug by Spirit’s wheels. Six outcrops and rocks were also analyzed as plausible source areas for the spherules and other particles observed in the soil around Home Plate, or when associated with large patches of soils. The rocks on Home Plate were covered by enough dust that RAT brushing was required to allow textures to be seen by the MI, such as the dark, moderately sorted and rounded grains (lapilli?) of the rock “Pecan Pie.” The MI also monitored the MER magnets and solar panels at the 2008 winter haven on the north side of Home Plate. After solar power was sufficient to allow Spirit to drive again, the MI was used to examine the silica-rich rock “Stapledon” just north of Home Plate. The texture of Stapledon appears similar to that seen in the silica-rich rocks on the east side of Home Plate, suggestive of secondary mineralization through precipitation from hydrothermal fluids. While plans for extracting Spirit from the sands of “Troy” are being made, the MI has been extensively used to examine the rocks and soils accessible to the instrument arm. These data show that moderately sorted, salty aggregate soils at depth are overlain by a thin crust near the present surface. These observations, along with MI images showing Spirit’s underbelly, are being used to inform extraction testing in the MER testbed at JPL. While the MI was not designed to take images of objects under the rover, the out-of-focus data still show what appears to be a rock touching the belly. Opportunity MI observations in Victoria crater show that hematite concretions are generally smaller and less spherical than those observed farther north on Meridiani Planum, despite similarities in the chemical composition of the rocks. This change in the concretions may be due to lateral differences in depositional environment or diagenesis, or may reflect vertical stratigraphic variations as Opportunity traversed up section. As Opportunity traverses south from Victoria crater, the MI has observed multiple outcrops and cobbles. Some of the cobbles, such as “Santorini” and “Kasos,” show textures that are consistent with the interpretation, based on chemical data, that they are meteorites. More recently, Opportunity studied the boulder “Block Island,” an iron-nickel meteorite. MI images of “Block Island” show triangular features that are interpreted as Widmanstätten patterns, commonly observed in this type of meteorite. The MI has also imaged skeleton-like metal protrusions on “Block Island” that appear to be the result of preferential weathering of interstitial material.
Ashley James W.
Cabrol Nathalie A.
Herkenhoff Ken E.
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