Sulfate reduction: a model for subsurface Martian life

by Denson, J.; Chevrier, V.; Sears, D.; Ivey, D. M.

ESA's Mars Express and NASA's Mars Exploration Rovers have discovered extensive deposits of sulfate minerals on the surface of Mars. These findings provide some of the most compelling evidence that there were once large deposits of liq. water on the martian surface. We have performed a kinetic study investigating the stability of MgSO4 brine solns. under simulated martian conditions. This included precise control of temp. (O°C), pressure (6-7 mbar) and atm. compn. (100% CO2). Our results indicate that highly concd. brines (20-25 wt%) dramatically alter the evapn./sublimation rates when compared to water/water ice, with a rate approx. 10 fold lower than expected. These concd. brines also promoted the existence of metastable liqs., which suggests a unique niche for martian life. Sulfate redn. is thought to be one of the earliest forms of respiration to arise on the early Earth. This is based on a wide range of evidence, including phylogenetic studies of present day sulfate reducers and isotopic fractionation studies of sulfur bearing minerals. Therefore sulfate-reducing microorganisms are an intriguing group to serve as a model for potential martian life. The ability of sulfate-reducing microorganisms to survive and potentially grow under simulated martian surface and subsurface conditions is currently being investigated. This research will explore the utility of sulfate redn. as a form of respiration for martian microbes, give valuable insight into possible biosignatures produced by such organisms on Mars, and provide an initial glimpse into the energetics of such a system.

Astronomical Society of the Pacific Conference Series
Bioastronomy 2007: Molecules, Microbes, and Extraterrestrial Life
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