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Science 3 July 2009:
Vol. 325. no. 5936, pp. 61 - 64
DOI: 10.1126/science.1172768
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Reports

Evidence for Calcium Carbonate at the Mars Phoenix Landing Site

W. V. Boynton,1,* D. W. Ming,2 S. P. Kounaves,3 S. M. M. Young,3,{dagger} R. E. Arvidson,4 M. H. Hecht,5 J. Hoffman,6 P. B. Niles,2 D. K. Hamara,1 R. C. Quinn,7 P. H. Smith,1 B. Sutter,10 D. C. Catling,8,9 R. V. Morris2

Carbonates are generally products of aqueous processes and may hold important clues about the history of liquid water on the surface of Mars. Calcium carbonate (approximately 3 to 5 weight percent) has been identified in the soils around the Phoenix landing site by scanning calorimetry showing an endothermic transition beginning around 725°C accompanied by evolution of carbon dioxide and by the ability of the soil to buffer pH against acid addition. Based on empirical kinetics, the amount of calcium carbonate is most consistent with formation in the past by the interaction of atmospheric carbon dioxide with liquid water films on particle surfaces.

1 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.
2 Johnson Space Center, Houston, TX 77058, USA.
3 Department of Chemistry, Tufts University, Medford, MA 02155, USA.
4 Department of Earth and Planetary Sciences, Washington University, Saint Louis, MO 63130, USA.
5 Jet Propulsion Laboratory, Pasadena, CA 91109, USA.
6 Department of Physics, University of Texas at Dallas, Richardson, TX 75083, USA.
7 SETI Institute, NASA Ames Research Center, Moffett Field, CA 94035, USA.
8 Department of Earth Sciences, University of Bristol, Bristol BS8 1RJ, UK.
9 Department of Earth and Space Sciences, University of Washington, Seattle, WA 98195, USA.
10 Jacobs Engineering and Science Contract Group, NASA Johnson Space Center, Houston, TX 77058, USA.

{dagger} Present address: Department of Chemistry, University of New Hampshire, Durham, NH 03824, USA.

* To whom correspondence should be addressed. E-mail: wboynton{at}LPL.Arizona.edu

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THIS ARTICLE HAS BEEN CITED BY OTHER ARTICLES:
H2O at the Phoenix Landing Site.
P. H. Smith, L. K. Tamppari, R. E. Arvidson, D. Bass, D. Blaney, W. V. Boynton, A. Carswell, D. C. Catling, B. C. Clark, T. Duck, et al. (2009)
Science 325, 58-61
   Abstract »    Full Text »    PDF »
Detection of Perchlorate and the Soluble Chemistry of Martian Soil at the Phoenix Lander Site.
M. H. Hecht, S. P. Kounaves, R. C. Quinn, S. J. West, S. M. M. Young, D. W. Ming, D. C. Catling, B. C. Clark, W. V. Boynton, J. Hoffman, et al. (2009)
Science 325, 64-67
   Abstract »    Full Text »    PDF »


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