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Science 30 May 2008:
Vol. 320. no. 5880, pp. 1204 - 1207
DOI: 10.1126/science.1155432
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Reports

Water Activity and the Challenge for Life on Early Mars

Nicholas J. Tosca,1* Andrew H. Knoll,1 Scott M. McLennan2

In situ and orbital exploration of the martian surface has shown that acidic, saline liquid water was intermittently available on ancient Mars. The habitability of these waters depends critically on water activity (Formula), a thermodynamic measure of salinity, which, for terrestrial organisms, has sharply defined limits. Using constraints on fluid chemistry and saline mineralogy based on martian data, we calculated the maximum Formula for Meridiani Planum and other environments where salts precipitated from martian brines. Our calculations indicate that the salinity of well-documented surface waters often exceeded levels tolerated by known terrestrial organisms.

1 Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA.
2 Department of Geosciences, State University of New York, Stony Brook, NY 11794, USA.

* To whom correspondence should be addressed. E-mail: ntosca{at}fas.harvard.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
How long was Meridiani Planum wet? Applying a jarosite stopwatch to determine the duration of aqueous diagenesis.
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Sulfate-Rich Eolian and Wet Interdune Deposits, Erebus Crater, Meridiani Planum, Mars.
J. M. Metz, J. P. Grotzinger, D. M. Rubin, K. W. Lewis, S. W. Squyres, and J. F. Bell III (2009)
Journal of Sedimentary Research 79, 247-264
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Acid production by FeSO4{middle dot}nH2O dissolution and implications for terrestrial and martian aquatic systems.
J. A. Hurowitz, N. J. Tosca, and M. D. Dyar (2009)
American Mineralogist 94, 409-414
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Ecophysiology of "Halarsenatibacter silvermanii" Strain SLAS-1T, gen. nov., sp. nov., a Facultative Chemoautotrophic Arsenate Respirer from Salt-Saturated Searles Lake, California.
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Appl. Envir. Microbiol. 75, 1950-1960
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Arid geomorphology: emerging research themes and new frontiers.
S. Tooth (2009)
Progress in Physical Geography 33, 251-287
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Orbital Identification of Carbonate-Bearing Rocks on Mars.
B. L. Ehlmann, J. F. Mustard, S. L. Murchie, F. Poulet, J. L. Bishop, A. J. Brown, W. M. Calvin, R. N. Clark, D. J. D. Marais, R. E. Milliken, et al. (2008)
Science 322, 1828-1832
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Science. ISSN 0036-8075 (print), 1095-9203 (online)