Mathematics – Logic
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p12a..04m&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #P12A-04
Mathematics
Logic
[1027] Geochemistry / Composition Of The Planets, [5410] Planetary Sciences: Solid Surface Planets / Composition, [5494] Planetary Sciences: Solid Surface Planets / Instruments And Techniques, [6225] Planetary Sciences: Solar System Objects / Mars
Scientific paper
Understanding the sulfur cycle on Mars is central to evaluating the history of surficial aqueous processes on that planet. The sulfur-rich nature of Martian soils was recognized with the first chemical analyses returned by Viking landers, and confirmed by subsequent rovers Pathfinder, Spirit and Opportunity. Existence of regions on Mars with elevated sulfate mineralogy has also been demonstrated by various orbital IR spectrometers. Nevertheless, the global distribution of S on the Martian surface has remained unknown. For example, the recent Phoenix mission failed to unambiguously identify any sulfate minerals in north polar soils. After seven years of orbital measurements, the Mars Odyssey Gamma Ray Spectrometer (GRS) has obtained sufficient data to produce a statistically useful map of S distributions in the Martian near surface for low- to mid-latitudes (i.e., excluding high-latitude areas with H-enrichment: the so-called H-mask). The surface of Mars is characterized by elevated S, but varying from <1% to >3%, and with highest concentrations being found at low latitudes. Global average S content is approximately 2%, similar to average Martian soils analyzed to date. The overall distribution of S abundances, using 5°X5° bins, is characterized by a near-Gaussian distribution, similar to the distributions of other elements across the Martian surface measured by GRS. Sulfur exhibits highly scattered but statistically significant (at 95% confidence) positive bivariate correlations with both hydrogen and chlorine. In detail, the nature of these correlations differs for northern and southern hemispheres; for example the most extreme S values are mostly restricted to the northern hemisphere and correlation coefficients are larger in the south. For low latitudes, where occurrence of near surface ice is least likely (30°N to 30°S) the slope of the hydrogen - sulfur linear correlation can be interpreted as reflecting structural and/or bound water in near-surface minerals. The average slope thus is equivalent to an average hydration state of approximately 2 for divalent cation sulfates (e.g., Ca-, Mg-, Fe(II)-sulfates), a value broadly consistent with expected thermodynamic stability in these regions. The sulfur-chlorine linear correlation is characterized by an approximately 0.3% Cl intercept, a value that is comparable to the intercept observed for sulfur-chlorine correlations in Martian basaltic soils. The large Cl intercept is consistent with differential mobility of S and Cl in the near surface environment, with Cl being preferentially concentrated nearest the surface. Differential dissolution - re-precipitation of chloride and sulfate minerals on a global scale could reflect low water activities in the near surface environment and thus have astrobiological relevance.
Boynton Willam V.
Hahn Brian C.
Karunatillake Suniti
McLennan Scott M.
Taylor Jacob
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