Reply to comment by Biemann and Bada on “Reanalysis of the Viking results suggests perchlorate and organics at midlatitudes on Mars”

摘要

Motivated by the discovery of soil perchlorate in the Martian Arctic by the Phoenix mission, we conducted new experiments with Mars-like soils from the Atacama Desert containing extremely low levels of soil organic carbon (32 ±6 ppm) and added magnesium perchlorate (1 wt%) using the Viking GC-MS protocol for the detection of soil organics [Navarro-González et al., 2010, 2011]. Our results demonstrated that nearly all the organics present in the soil were combusted to water and carbon dioxide, but a small amount was chlorinated, forming 400 ppb of chloromethane and 5 ppb of dichloromethane at 500°C. Kinetic modeling provided additional support for the combustion and chlorination of soil organics in the presence of perchlorate. These chlorohydrocarbons were detected by the Viking GC-MS experiments when the Martian soil was analyzed but they were considered to be terrestrial contaminants, although they had not been detected at those levels in the blank runs. Biemann and Bada [2011] argue that our conclusions are contradicted by our own experimental data but they do not provide any experimental or theoretical grounds for this assertion.Furthermore, the analysis provided here demonstrates that it is unlikely that remnants of cleaning fluids could have persisted after the rigorous cleaning protocol performed by the Viking mission and thereby explain the detection of chlorinated compounds. Our results have important implications for future Mars research and the development of new instruments and methods that will search for Martian organics.