Physics
Scientific paper
May 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agusm.p32a..01d&link_type=abstract
American Geophysical Union, Spring Meeting 2005, abstract #P32A-01
Physics
5400 Planetology: Solid Surface Planets, 5415 Erosion And Weathering, 5421 Interactions With Particles And Fields, 5470 Surface Materials And Properties
Scientific paper
The landscape in Meridiani Planum encountered by the Rover Opportunity is different to all previous Mars landing sites. While those locations look like typical unsorted alluvials, Meridiani Planum consists of sorted sands with aeolian features like small dunes and desert pavements in places. Chemical compositions of soils and rocks at Gusev crater and Meridiani Planum were measured by the Alpha Proton X-Ray Spectrometer (APXS) [1, 2]. At Meridiani Planum all soils and outcrops have a higher mean Fe/Si ratio of 0.75 compared to rocks and soils in Gusev crater with a mean Fe/Si of 0.57. The enrichment of Fe results from an admixture of hematite (Fe2O3) as determined in-situ by the Mössbauer spectrometer (MB) [3]. The formation of hematite is an indicator for aqueous activities under oxidizing conditions. The highest portion of this mineral was found in the spherical grains, also nicknamed `blueberries', which cover most place at the landing site. These spherules were also found in rock exposures in Eagle crater to about 2 % by volume and were interpreted as concretions that formed by precipitation from aqueous fluids inside sedimentary rocks [4]. At Gusev crater no hematite was observed until sol 90 except for layering on a rock. However, about three months later at the foot of the Columbia Hills the MB detected hematite in a rock, dubbed `Pot of Gold'. Our investigations of hematite bearing materials, measured by APXS, MB, and Microscopic Imager (MI) [5], provide an integrated view of different occurrences of hematite on the Martian surface. Ratios of Fe to Mn are compared with Fe concentrations for various soils and outcrops in Meridiani Planum and Gusev crater. Most samples cluster at a mean Fe/Mn ratio of about 50 and range in Fe from 12 to 17 wt. %. Exceptions are found for those Meridiani Planum soils that have very high Fe contents of about 26 wt. %, such as targets dubbed `JackRussell', `FredRipple', and `Berry Bowl full', all showing Fe/Mn ratios of about 110. Based on APXS measurements we cannot distinguish, whether spherules consist of pure hematite or carry a thin layer of hematite. All these high hematite bearing soils are top surface samples, while corresponding subsurface soil samples or soils disturbed by rover wheels have low hematite contents. The very high Fe/Mn ratios of three undisturbed samples together with very high hematite contents suggest the presence of a hematite-rich top layer irrespectively of shape and area coverage of spherules or fragments and could be interpreted as a surface coating similar to terrestrial surface coatings. In the hematite rich outcrops with the same Fe/Mn ratio as found for the soil samples the formation of the main portion of fine dispersed hematite must be an isochemical re-crystallization process under strongly oxidizing conditions. [1] Gellert, R. et al. (2004) Science, 305, 829-832. [2] Rieder, R. et al. (2004) Science, 306, 1746-1749. [3] Klingelhöfer, G. et al. (2004) Science, 306, 1740-1745. [4] Squyres, S, et al. (2004) Science, 306, 1698-1703. [5] Herkenhoff, K. E. et al. (2004) Science, 306, 1727-1730.
Brückner James
Dreibus Gerlind
Jagoutz Emil
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