DPS 35th Meeting, 1-6 September 2003
Session 9. Mars Surface I
Oral, Chairs: E. R. Kraal and R. C. Quinn, Wednesday, September 3, 2003, 10:30am-12:00noon, DeAnza III

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[9.09] Organic chemical decomposition in the Atacama Desert and on the surface of Mars: A comparison of potential reaction mechanisms

R.C. Quinn (SETI Institute, NASA Ames), F.J. Grunthaner (JPL), C.L. Taylor (SETI Institute, NASA Ames), A.P. Zent, C.P. McKay (NASA Ames), B. Gomez-Silva (Universidad de Antofagasta, Chile), J.L. Bada (U.C. San Diego)

The liquid phase pH and Eh kinetic profile has been measured for soil samples collected at 24.06 S latitude 69.85 W longitude in the Chilean Atacama Desert. Since it is our desire to better understand the results of Viking Biology Experiments, the Eh and pH values achieved upon the initial wetting of the soil is key to understanding the redox chemistry of the system. Complementary studies of culturable bacteria in the Atacama Desert indicate that the numbers of heterotrophic bacteria and diversity are a function of local water availability. In the driest regions (24 S) there are sites where no bacteria could be isolated [1]. Soils collected from this region were reported to be essentially free of organic matter based on flash pyrolysis GCMS analysis [2]. Correspondingly, the Viking Gas Exchange (GEx) and Labeled Release (LR) experiments were unable to demonstrate the presence of culturable bacteria, and the pyrolysis-GCMS was unable to detect organic compounds [3].

With water addition, surface samples collected at the site show a shift from an acidic to a more basic pH. This trend is consistent with the pH shift (derived from CO2 uptake) seen in the Viking GEx. The measured soil Eh and pH values along with measurements of atmospheric ozone, nitrogen oxides, and sulfur dioxide suggest an aqueous, inorganic-acid mediated reaction resulting in organic compound decomposition at the soil surface. These results and potential reaction mechanisms will be discussed in relation to the reactive soil chemistry seen in the Viking Biology Experiments and current theories of organic chemical decomposition processes that may be occurring on Mars.

This work was supported by the NASA ASTEP Program.

References: [1] Clements M. C. et al. (2002) 2nd Astrobiology Conference Abstract NASA Ames. [2] Navarro-Gonzalez R. et al. (2002) 2nd Astrobiology Conference Abstract NASA Ames. [3] Klein H. P. (1979) Rev. Geophys. Space Phys. 17, 1655-1662.

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