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Title:
One Martian Year of in Situ Chemistry by the APXS on Board the Mars Exploration Rover Opportunity at Meridiani Planum
Authors:
Brueckner, J.; Dreibus, G.; Gellert, R.; Clark, B. C.; Klingelhoefer, G.; Lugmair, G.; Ming, D.; Rieder, R.; Waenke, H.; Yen, A.; Zipfel, J.
Affiliation:
AA(Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany ; ), AB(Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany ; ), AC(Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany ; Department of Physics, University of Guelph, Guelph, ON N1G2W1 Canada ; ), AD(Lockheed Martin Corporation, MS S8000, PO Box 179, Littleton, CO 80127 United States ; ), AE(Institut fuer Inorganische und Analytische Chemie, Johannes Gutenberg-Universitaet, Staudinger Weg 9, Mainz, D-55099 Germany ; ), AF(Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany ; ), AG(NASA Johnson Space Center, Mail Code SX3, 2101 NASA Road 1, Houston, TX 77058-2906 United States ; ), AH(Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany ; ), AI(Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany ; ), AJ(Jet Propulsion Laboratory, MS 183-501, 4800 Oak Grove Dr, Pasadena, CA 91104 United States ; ), AK(Max-Planck-Institut fuer Chemie, Postfach 3060, Mainz, D-55020 Germany ; Forschungsinstitut und Naturmuseum Senckenberg, Senckenberganlage 25, Frankfurt, D-60325 Germany ; )
Publication:
American Geophysical Union, Fall Meeting 2005, abstract #P12A-06
Publication Date:
12/2005
Origin:
AGU
AGU Keywords:
5410 Composition (1060, 3672)
Bibliographic Code:
2005AGUFM.P12A..06B

Abstract

Two in-situ instruments, the Alpha Particle X-ray Spectrometer (APXS) and the Moessbauer Spectrometer (MB), gathered geochemical and mineralogical data along the traverse of the Mars Exploration Rover Opportunity at Meridiani Planum. Eagle crater, the landing site of the rover, contains undisturbed soils that resemble those at Gusev crater; however, the Fe, Ni, and Cr contents and Fe/Si ratios of Meridiani soils are higher than those of Gusev soils. The enrichment of Fe results from an admixture of the mineral hematite as determined by MB. This mineral occurs as a finely disseminated component of the outcrop rocks as well as in mm- to several mm-sized spherules, nicknamed blueberries, which are spread at the landing site and along the several kilometers traverse to the Erebus crater. The formation of hematite is typically an indicator for aqueous activity under oxidizing conditions. Light-toned layered outcrops were discovered in Eagle crater and later in other craters, as well as along the rover's traverse. Most of these undisturbed rock surfaces have a factor of 2 to 3 higher S concentrations compared to the soils. In Eagle crater, ground rock surfaces (exposed by the Rock Abrasion Tool, or RAT) showed even higher S contents of up to 9.5 weight percent. Assuming all SO3 is bound to Mg and Ca sulfates and, according to MB data, to ferric sulfates, mainly jarosite, these rocks contain about 40 weight percent sulfates. High concentrations of Br were discovered in some soils excavated with the rover wheels and rocks ground with the RAT. The high abundances of S and Br in these rocks point to ancient occurrence of acidified water and the formation of brines, which could have been occasionally evaporated. Small quantities of the hematite-rich spherules (ca. 2 volume percent) were found in the rocks of Eagle crater. The acidic conditions during the formation of the hematitic spherules in the rocks as concretions allowed co-precipitation of Fe2O3 and NiO but no MnO. When the rover was climbing into Endurance crater, a full stratigraphic sequence was measured with APXS and MB. Large enrichments of Cl were not accompanied by Br and S. The major elements varied within small ranges except for lower layers, where Mg is depleted together with S but Si and Al are enriched. Two rocks on the plains, analyzed by APXS and MB, are related to known meteorite classes: 'Bounce Rock' is similar in chemistry and mineralogy to basaltic shergottites, a subgroup of martian meteorites, whereas 'Heat Shield Rock' with high Fe and Ni concentrations is an iron meteorite. On the rover's journey from Endurance crater to Erebus crater, light-toned rocks were encountered whose chemical compositions resemble those of the well-known rocks of Eagle and Endurance craters, indicating that the sulfur-rich deposits occur on a scale exceeding several kilometers, consistent with evidence from orbital spacecraft.
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