Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.p23b..07d&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #P23B-07
Physics
6225 Mars, 3672 Planetary Mineralogy And Petrology (5410), 1060 Planetary Geochemistry (5405, 5410, 5704, 5709, 6005, 6008), 0330 Geochemical Cycles, 0400 Biogeosciences
Scientific paper
Spirit's observations address whether the Gusev crater site provided the ingredients ("biogenic" elements: C, O, H, S, N, P and key metals) and conditions (useful energy, liquid water, etc.) necessary for life as we know it. In concert with earlier observations of martian meteorites and the martian atmosphere, Spirit observed that virtually all of the major biogenic elements appear to be readily available. An assessment of energy sources for life must consider whether liquid water and favorable environments were simultaneously present, thus enabling life to utilize that energy. For example, the solar energy flux at the surface could sustain photosynthesis, but it is uncertain whether liquid water was also present at the surface at a chemical potential sufficient for life. However, aqueous alteration of the mineral olivine releases H2, which, together with oxidants as mild as CO2, provides chemical energy. Olivine rich basalts dominate the local rock population. Normative olivine abundances in the rocks Adirondack, Humphrey and Mazatzal lie in the range 21 to 36 wt. percent. Low rock strengths (shown by the RAT), textures (Microscopic Imager) and mineralogy (Moessbauer) and elemental abundances (APXS) indicate that these rocks have been altered by water to varying degrees. Thus subsurface basaltic environments had the capacity to provide energy to "chemoautotrophs," which are microorganisms that utilize chemical redox reactions to obtain energy and to convert CO2 to biomass. The distribution and duration of potentially habitable conditions in the near-subsurface environment remain uncertain, but Spirit has shown that a broad range of scenarios existed. Laguna hollow is a relatively recent secondary impact crater filled with dust and drift material. A trench dug in the hollow revealed that soluble salts and insoluble constituents were uniformly physically mixed together and thus were deposited and stored under very dry conditions. In contrast, Spirit trenched the much older, more mature "intercrater plains material" (e.g., "The Boroughs" trench) and found substantially elevated Mg and S abundances at depth, consistent with their mobilization by water. Weathering of olivine basalts in this subsurface environment might have provided chemical energy for life, however it is uncertain whether the ionic strength of the aqueous solution was sufficiently low to sustain Earth-like metabolism. However, the extensively altered rocks at West Spur, Columbia Hills indicate that, sometime in the past, conditions probably had the capacity to sustain chemoautotrophic life.
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