DPS 2001 meeting, November 2001
Session 48. Mars Surface
Oral, Chairs: N. Barlow, J. Bell III, Friday, November 30, 2001, 4:30-6:40pm, Regency E

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[48.01] Geochemical energy potentially available to organisms in martian hydrothermal systems.

E.S. Varnes, B.M. Jakosky (U. of Colorado Dept. of Geological Sciences and Laboratory for Atmospheric and Space Physics), T.M. McCollom (Woods Hole Oceanographic Institute)

Although a global average of energy available to potentially support life from chemosynthesis on Mars has been estimated, issues of how the energy is distributed and which environments have the greatest potential to support life remain unresolved. We have begun to address these questions by developing numerical geochemical models of martian hydrothermal systems using the software package EQ3/6.

In order to model hydrothermal systems, the elemental composition of the initial fluid (the groundwater) and the initial host rock with which it interacts must be defined. The host rock was defined using the composition of LEW 88516, which is similar to the martian mantle. This host rock was reacted at high temperature (350 deg C) with a series of groundwaters. Groundwaters are either pure water in equilibrium with present martian atmosphere or in equilibrium with Pathfinder-composition soils and the atmosphere. The hot fluid resulting from the rock/groundwater reaction was then reacted with increments of fresh groundwater, simulating the mixing that occurs in hydrothermal systems. During mixing, oxidation and reduction reactions are kinetically inhibited; organisms may exploit this inhibition to derive metabolic energy. The maximum amount of energy an organism can obtain from a given reaction is determined from the Gibbs free energy of that reaction. For each model run, we have calculated the Gibbs free energy of reactions that are important for terrestrial chemosynthetic organisms and likely representative for putative martians. Our results indicate that substantial amounts of energy may be derived from these reactions, but they depend sensitively on the oxidation state of the groundwater and whether saturated species precipitate to equilibrium. Thus, it is unknown whether sufficient energy is available to support martian life, although it is likely that suitable environments exist.

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