José de la Rosa

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

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.

Mars-Like Soils in the Yungay Area, the Driest Core of the Atacama Desert in Northern Chile

The data obtained from the Viking lander’s analyses of soils on Mars were unexpected. First, was the finding that when soil samples were exposed to water vapor in the gas exchange experiment (GE) there was rapid release of molecular oxygen, at levels of 70-770 nmole g-1 (Oyama and Berdahl, 1977). The next puzzling result was that organic material in the labeled release experiment (LR) was consumed as would be expected if life would have been present (Levin and Straat, 1977). Lastly, there were no organic materials at levels of part-per-billion (ppb), as measured by pyrolysis-gas chromatography-mass spectrometry (pyr-GC-MS) detected (Biemann et al., 1977); which were in apparent contradiction with the presence of life as detected by the LR experiment. The reactivity of the martian soil is currently believed to result from the presence of one or more inorganic oxidants (e.g., superoxides, peroxides, or peroxynitrates) at the part-per-million (ppm) level. The absence of organics in the soils results from their oxidation by such oxidants and/or direct ultraviolet radiation damage (McKay et al., 1998).