Assessing the Nature, Distribution and Duration of Noachian Habitable Environments

Details Assessing the Nature, Distribution and Duration of Noachian Habitable Environments Assessing the Nature, Distribution and Duration of Noachian Habitable Environments

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufm.p43d..08d&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #P43D-08

Biology

0406 Astrobiology And Extraterrestrial Materials, 0456 Life In Extreme Environments, 5220 Hydrothermal Systems And Weathering On Other Planets, 5419 Hydrology And Fluvial Processes, 6225 Mars

Scientific paper

Life as we know it indicates that habitable environments must simultaneously provide liquid water, conditions favorable for the assembly of complex organic molecules, nutrients for cellular constituents, and sources of energy that can sustain metabolism. These requirements must be met simultaneously and perhaps at least intermittently over geologically long periods. Recent missions indicate that liquid water probably persisted in the shallow subsurface during the Noachian. Surface waters occurred at least locally as indicated by geomorphologic features observed by orbiters and by analyses of Meridiani bedrock by MER Opportunity. Atmospheric precipitation and springs probably sustained surface waters at least intermittently during the Noachian. However whether lakes or a northern ocean persisted for long periods remains controversial. Theoretical models and surface geomorphology indicate that extensive groundwater probably persisted for geologically long times. Observations of spectral features of methane in the atmosphere indicate that groundwater might exist even today. Perhaps most challenging for achieving habitable conditions on Mars has been the requirement that liquid water and biologically useful sources of energy occur simultaneously. Because liquid water has been unstable at the martian surface for most of its history, both solar energy and liquid water have probably not been simultaneously available to sustain photosynthesis for most of Mars' history. Fortunately microorganisms also can obtain energy from iron and sulfur redox reactions in the absence of light. MER Spirit found evidence that iron oxidation might have occurred simultaneously with the aqueous alteration of rocks. MEX, MRO and MER documented extensive sulfates that might have derived at least in part from volcanic sulfur emissions oxidized under aqueous conditions. Perhaps most challenging for Mars exploration will be to visit sites where habitable environments once persisted and where their evidence has been well preserved. On Earth, phyllosilicates, carbonates, silica and evaporite minerals have retained remarkable records of our early biosphere. MEX, MRO and MER have revealed sites where such minerals occur and therefore perhaps also where evidence of ancient habitable environments has been preserved.

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