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The Limitations on Organic Detection in Mars-Like Soils by Thermal Volatilization-Gas Chromatography-MS and Their Implications for the Viking Results
Rafael Navarro-González, Karina F. Navarro, José de la Rosa, Enrique Iñiguez, Paola Molina, Luis D. Miranda, Pedro Morales, Edith Cienfuegos, Patrice Coll, François Raulin, Ricardo Amils and Christopher P. McKay
Proceedings of the National Academy of Sciences of the United States of America
Vol. 103, No. 44 (Oct. 31, 2006), pp. 16089-16094
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/30052117
Page Count: 6
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The failure of Viking Lander thermal volatilization (TV) (without or with thermal degradation)-gas chromatography (GC)-MS experiments to detect organics suggests chemical rather than biological interpretations for the reactivity of the martian soil. Here, we report that TV-GC-MS may be blind to low levels of organics on Mars. A comparison between TV-GC-MS and total organics has been conducted for a variety of Mars analog soils. In the Antarctic Dry Valleys and the Atacama and Libyan Deserts we find 10-90 μg of refractory or graphitic carbon per gram of soil, which would have been undetectable by the Viking TV-GC-MS. In iron-containing soils (jarosites from Rio Tinto and Panoche Valley) and the Mars simulant (palogonite), oxidation of the organic material to carbon dioxide (CO₂) by iron oxides and/or their salts drastically attenuates the detection of organics. The release of 50-700 ppm of CO₂ by TV-GC-MS in the Viking analysis may indicate that an oxidation of organic material took place. Therefore, the martian surface could have several orders of magnitude more organics than the stated Viking detection limit. Because of the simplicity of sample handling, TV-GC-MS is still considered the standard method for organic detection on future Mars missions. We suggest that the design of future organic instruments for Mars should include other methods to be able to detect extinct and/or extant life.
Proceedings of the National Academy of Sciences of the United States of America © 2006 National Academy of Sciences