Other
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.p53a1484b&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #P53A-1484
Other
[5410] Planetary Sciences: Solid Surface Planets / Composition
Scientific paper
Numerous soils were investigated at the landing sites of the two NASA Mars Exploration Rovers (MER) Spirit and Opportunity. In-situ measurements were done by the Alpha Particle X-ray Spectrometer (APXS) to determine the chemical composition of soils and by the Mössbauer Spectrometer (MB) to provide data on their iron mineralogy. Measurements were made on undisturbed and disturbed (by rover wheels) soils and soil trenches. Remote sensing data by the Panoramic Camera and the Mini-TES provided information on the presence of additional phases, but, are not covered, here. The Mg/Si to Al/Si ratios reveal that most soils have a comparable composition independent of the landing site A (Gusev Crater) or B (Meridiani Planum). A more careful look shows that the B soils have a somewhat lower ratio than the A ones. The B soils also have a generally higher Fe concentration. Mössbauer measurements explain this by the occurrence of hematite-rich spherules in the soils, or hematite and magnetite in the dust. In fact, there is a mixing line between Fe and Si indicating the dilution of Si (and related elements) by the addition of hematite. The formation of hematite was an isochemical process and is characteristic for site B. These and other observations point to a dual process for the formation of most of the soils. One component, the top most layer is influenced by aeolian processes. Vast dust storms transport very fine material (grain size in the lower micrometer regime) over large distances. This can be best seen for the rather constant ratio of Cl and S, two very volatile elements, at both sites. Their global distribution points to a volcanic source: exhalation during eruptions. The differences in Fe contents have their origin in local contributions. Most soil grains are too large for airborne transport and thus transported by saltation. Chemical inhomogeneities, as seen by orbital gamma-ray spectroscopic measurements, even out at least for the visited landing sites outside the Polar Regions (Viking 1 and 2, Mars Pathfinder, MER). The rather similar compositions reveal that the general sources of the soils are similar and close to a basaltic or mafic composition, probably representing the general crustal composition of Mars. At site A, soils with significant deviations in chemistry and mineralogy were encountered. They are usually enriched in one or two elements, in the form of sulfates or siliceous components, discovered by plowing action of Spirit’s stuck wheel, and formed by very specific ancient weathering or hydrothermal processes. In summary, the investigation of soils can reveal either local processes (enrichment of salts by action of water), regional processes (formation of hematite), or global processes (aeolian transport of e.g. Cl and S) at the surface of Mars.
Athena Science Team
Brueckner Johannes
Fleischer Iris
Gellert Ralf
Klingelhoefer G.
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