Mathematics – Logic
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p11e..03g&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #P11E-03
Mathematics
Logic
1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 5415 Erosion And Weathering, 5419 Hydrology And Fluvial Processes, 5470 Surface Materials And Properties, 6225 Mars
Scientific paper
MER APXS data of soils at the Gusev [1,2] and Meridiani [2,3] landing sites show positive correlations of sulfur, chlorine and phosphorus. These 3 chemical elements also correlate positively with the Mossbauer determination of nano-phase iron oxide (Np-ox) component in the soils [2, 4, 5]. Yen et al. show that Pancam spectra of bright dust at both landing sites is correlated with higher sulfur contents, and that dark soils are low-sulfur, basalt-rich endmembers. Yen et al. argue that the bright dust is a globally homogeneous soil. Yen et al. also report Br heterogeneities in soil trenches, which they ascribe to a mechanism similar to acid-fog weathering, wherein diurnal or seasonal cycling of thin films of acidic water ultimately lead to Br enrichments in subsurface soils. Haskin et al. report Mg, Cl, Br, and S correlations in a rover-dug trench at the Gusev landing site (The Boroughs), which is also ascribed to diurnal or seasonal cycling of thin films of acidic water. Thus, it appears that the acid-film mechanism of weathering leads to heterogeneities in mobile soil components (S, Cl, and Br), likely due to the different solubilities of sulfates, chlorides, and bromides. Gellert et al. and Rieder et al. both argue that phosphorus in the Martian soils is derived by the weathering of local rock by acidic brines. Yet, the evidence from Br and from subsurface deposits suggests that acidic weathering on Mars has led to heterogeneities in soluble elements in Martian soils. The globally homogeneous bright dust, which appears to have similar elemental ratios of P/Cl, S/Cl, and P/S, as well as P/Np-ox, Cl/Np-ox, and S/Np-ox, at both Gusev and Meridiani landing sites, argues that these ratios were formed by a similar process, which led to homogeneity, not heterogeneity of these components. The original source of sulfur and chlorine enrichments on the Martian surface may be due to the excess volatiles or solubles from accretion, or volcanic degassing. Phosphorus is a rock component and cannot be derived by volcanic degassing and must ultimately be derived by weathering of igneous rocks. For phosphorus to be a significant aqueous component (as suggested by correlations with S and Cl), an acidic fluid is likely necessary, due to the low solubilities of Ca-phosphate minerals in neutral to basic solutions (this assumes that phosphate in Martian fluids is controlled by mineral solubilities). On Earth, phosphorus concentrations are generally low in aqueous fluids, due to biological uptake. If Martian fluids were rich in phosphorus, this is a potential indicator for a lack of biological activity. A large, acidic aqueous reservoir (such as an ocean) is needed to homogenize P, S, and Cl, and to lead to all 3 of these elements positively correlating with Np-ox at both landing sites. We propose that the Martian soils contain a component of Np-ox encrusted with salts of phosphate (possibly sorbed P), sulfate, and chloride. This component was likely formed in an acidic ocean. [1] Gellert, R. et al. Science 305, 829 (2004) [2] Yen et al. Nature 436, 49 (2005) [3] Rieder, R. et al. Science 306, 1746 (2004) [4] Morris, R. V. et al. Science 305, 833-836 (2004) [5] Klingelhofer G. et al. Science 306, 1740-1745 (2004) [6] Haskin, L. A. et al. Nature 436, 66 (2005)
Blake Ruth E.
Greenwood James Paul
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