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 liquid water on the martian surface. We have performed a ki-netic study investigating the stability of MgSO_4 brine solutions under simulated martian conditions. This included precise control of temperature (O ° C), pres-sure (6-7 mbar) and atmospheric composition (100% CO_2). Our results indicate that highly concentrated brines (20-25 wt%) dramatically alter the evapora-tion/sublimation rates when compared to water/water ice, with a rate approx-imately 10 fold lower than expected. These concentrated brines also promoted the existence of metastable liquids, which suggests a unique niche for martian life. Sulfate reduction 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 abil-ity of sulfate-reducing microorganisms to survive and potentially grow under simulated martian surface and subsurface conditions is currently being investi-gated. This research will explore the utility of sulfate reduction as a form of respiration for martian microbes, give valuable insight into possible biosigna-tures produced by such organisms on Mars, and provide an initial glimpse into the energetics of such a system.
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