Mathematics – Logic
Scientific paper
Dec 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p43b1405g&link_type=abstract
American Geophysical Union, Fall Meeting 2008, abstract #P43B-1405
Mathematics
Logic
5410 Composition (1060, 3672), 5494 Instruments And Techniques, 6225 Mars
Scientific paper
The Alpha-Particle-X-ray Spectrometer (APXS) is part of the in-situ payload of the Mars Exploration Rovers (MER). It determined so far the elemental composition of ~300 soil and rock samples on both landing sites along the traverse. The composition is determined by x-ray spectroscopy and usually 16 elements from Sodium to Bromine are detected with detection limits down to ~20 ppm for Bromine. One of the most amazing findings at Meridiani Planum is the high sulfur content of the bedrock. It contains typically about 10% sulfur by weight, or rather 25% SO3 taking overwhelming mineralogical evidence into account that the sulfur is present as sulfate. The best samples to follow the overall sulfate content along the meanwhile 10 kilometer traverse are abraded samples, cleaned of loose soil, dust and possible altered rinds with the Rock Abrasion Tool (RAT). So far, 35 abraded samples were measured beginning in the ~10 meter impact crater Eagle, the 100 meter crater Endurance and further 5 km south to the 800 meter crater Victoria. The overall composition of these bulk samples is astonishingly constant, with certain important exceptions. Besides the high Sulfur, mainly Magnesium, Iron and to lesser extend Calcium are enriched in the remaining matrix, while Si and Al and most other elements are diluted compared to typical Martian materials like the soil. However, during the ingress into Endurance, and recently also into Victoria a remarkably similar parallel decrease of Mg and S was detected. This decrease by approximately 25% with a very good molar match for MgSO4 - with unknown hydration degree - is accompanied in both craters by an increase of Chlorine by a factor of ~3. The observed layering of likely very soluble minerals, Magnesium Sulfates and Chlorides - with so far no obvious accompanying Cation - observed in two impact craters about 5 km apart is evidence for a long ranging leveling interaction with water during the formation of Meridiani - or for shorter periods of time after these craters were created by impact. The parallel decrease of Mg and S and the nearly parallel, but steeper increase of Cl are very smooth over 11 abraded samples during the ingress into Endurance. In Victoria only 5 samples could be abraded. However, after a statistical significant trend in the first samples was already visible, the last and deepest reachable spot (Gilbert) in Victoria shows the clearest resemblance of the trends observed in Endurance. Bromine inversely correlates with Chlorine during the ingress, although the trend is more variable. The abundance of Sulfur, Chlorine and Bromine, is readily detectable by the APXS with very good precision and repeatability along the traverse on both MER rover landing sites. It reveals the different past environments in Gusev Crater and Meridiani Planum and provided ground truth for orbiter measurements. While in Meridiani the high Sulfur content of bedrock is very constant over kilometers but dipping in deeper layers, in Gusev Crater localized subsurface soil spots of highly enriched ferric sulfates and accompanying near pure Silica deposits are identified. The basaltic soil at both landing sites is very similar and contains about 6 % SO3, very variable and correlated with Chlorine.
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