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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.

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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_2O, we conclude that surface geochemical processes would have affected the redox state of the early martian atmosphere.

Item Type:Article
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URLURL TypeDescription DOIArticle
Hurowitz, Joel A.0000-0002-5857-8652
Fischer, Woodward W.0000-0002-8836-3054
Milliken, Ralph E.0000-0003-3240-4918
Additional Information:© 2010 Macmillan Publishers Limited. Received 28 October 2009; accepted 26 February 2010; published online 4 April 2010. Research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (J.A.H., R.E.M.). This work was also supported by the California Institute of Technology (W.W.F.) and by an Origins Initiative Postdoctoral Fellowship (N.J.T.). The authors thank Y. Yung, N. Heavens and J. Wilson for constructive comments. Author contributions: J.A.H. carried out data analysis, modelling and wrote the paper, W.W.F. and J.A.H. conceived the study, N.J.T. and R.E.M. contributed to modelling and W.W.F., N.J.T. and R.E.M. contributed to writing.
Funding AgencyGrant Number
Origins Initiative Postdoctoral FellowshipUNSPECIFIED
Subject Keywords:geochemistry; planetary science
Issue or Number:5
Record Number:CaltechAUTHORS:20100526-081809534
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:18444
Deposited By: Tony Diaz
Deposited On:19 Jun 2010 02:13
Last Modified:09 Mar 2020 13:19

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