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Published online on October 23, 2006, 10.1073/pnas.0604210103 OPEN ACCESS ARTICLE


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Chemistry
The limitations on organic detection in Mars-like soils by thermal volatilization-gas chromatography-MS and their implications for the Viking results

( astrobiology | detection of organics | search for martian life | extreme environments | deserts )

Rafael Navarro-González *{dagger}, Karina F. Navarro *, José de la Rosa *, Enrique Iñiguez *, Paola Molina *, Luis D. Miranda {ddagger}, Pedro Morales {sect}, Edith Cienfuegos {sect}, Patrice Coll ¶, François Raulin ¶, Ricardo Amils ||, and Christopher P. McKay **

*Laboratorio de Química de Plasmas y Estudios Planetarios, Instituto de Ciencias Nucleares, and Institutos de {ddagger}Química and {sect}Geología, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, P.O. Box 70-543, 04510 México D.F., Mexico; Laboratoire Interuniversitaire des Systèmes Atmosphériques, Unité Mixte de Recherche 7583, Centre National de la Recherche Scientifique, Université Paris 12-Val de Marne and Université Paris 7-Denis Diderot, 61 Avenue du Général de Gaulle 94010, Créteil Cedex, France; ||Centro de Astrobiología, Consejo Superior de Investigaciones Científicas/Instituto Nacional de Tecnica Aeroespacial, Torrejón de Ardoz, 28850 Madrid, Spain; and **Space Science Division, Ames Research Center, National Aeronautics and Space Administration, Moffett Field, CA 94035-1000

Edited by Leslie Orgel, The Salk Institute for Biological Studies, La Jolla, CA, and approved September 11, 2006 (received for review May 21, 2006)

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.

Author contributions: R.N.-G. and C.P.M. designed research; R.N.-G., K.F.N., J.d.l.R., P. Molina, and E.I. performed research; R.N.-G., K.F.N., L.D.M., P. Morales, E.C., P.C., F.R., R.A., and C.P.M. contributed new reagents/analytic tools; R.N.-G., K.F.N., and C.P.M. analyzed data; and R.N.-G. and C.P.M. wrote the paper.

The authors declare no conflict of interest.

Freely available online through the PNAS open access option.

{dagger}To whom correspondence should be addressed.

Rafael Navarro-González, E-mail: navarro{at}nucleares.unam.mx

www.pnas.org/cgi/doi/10.1073/pnas.0604210103
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