Origin of acidic surface waters and the evolution of atmospheric chemistry on early Mars

Hurowitz, Joel A. and Fischer, Woodward W. and Tosca, Nicholas J. and Milliken, Ralph E. (2010) Origin of acidic surface waters and the evolution of atmospheric chemistry on early Mars. Nature Geoscience, 3 (5). pp. 323-326. ISSN 1752-0894, 1752-0908 DOI 10.1038/ngeo831

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Abstract

Observations from in situ experiments and planetary orbiters have shown that the sedimentary rocks found at Meridiani Planum, Mars were formed in the presence of acidic surface waters. The water was thought to be brought to the surface by groundwater upwelling, and may represent the last vestiges of the widespread occurrence of liquid water on Mars. However, it is unclear why the surface waters were acidic. Here we use geochemical calculations, constrained by chemical and mineralogical data from the Mars Exploration Rover Opportunity, to show that Fe oxidation and the precipitation of oxidized iron (Fe 3+) minerals generate excess acid with respect to the amount of base anions available in the rocks present in outcrop. We suggest that subsurface waters of near-neutral pH and rich in Fe 2+ were rapidly acidified as iron was oxidized on exposure to O 2 or photo-oxidized by ultraviolet radiation at the martian surface. Temporal variation in surface acidity would have been controlled by the availability of liquid water, and as such, low-pH fluids could be a natural consequence of the aridification of the martian surface. Finally, because iron oxidation at Meridiani would have generated large amounts of gaseous H 2, ultimately derived from the reduction of H 2 O, we conclude that surface geochemical processes would have affected the redox state of the early martian atmosphere.

Item Type: Article
Uncontrolled Keywords: 2010AREP; IA59
Subjects: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Divisions: 01 - Climate Change and Earth-Ocean Atmosphere Systems
Journal or Publication Title: Nature Geoscience
Volume: 3
Page Range: pp. 323-326
Identification Number: 10.1038/ngeo831
Depositing User: Sarah Humbert
Date Deposited: 31 Jan 2012 08:43
Last Modified: 23 Jul 2013 10:03
URI: http://eprints.esc.cam.ac.uk/id/eprint/2350

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