January 1, 2015.
The Viking missions to Mars, which took place in the 1970’s, performed several experiments on martian soil in an attempt to discern if there was microbial life present. In one set of experiments, a nutrient solution containing amino acids and organic substrates tagged with carbon-14 was injected into sample cells containing martian soil, and the evolution of labeled CO2 was monitored. The evolution of labeled CO2 indicated that there was a process occurring that broke down the nutrients in solution and released CO2 as a byproduct. Cellular metabolism releases CO2, so this result supported the idea of microbial life on Mars. However, other results did not support this explanation; after an initial spike there was no additional activity when more nutrient solution was added, but instead the concentration of CO2 in the test cell decreased. If biological processes were responsible for CO2 evolution than the concentration of CO2 shoul increase. It was apparent there were explanations other than biology, such as the presence of strong oxidizers in martian soil; peroxides and superoxides were proposed. When the Phoenix mission landed on Mars in 2008, it conducted experiments that showed that martian soil was ~.5% by mass perchlorate. Experiments have shown that perchlorate exposed to radiation (as it would be in martian soil, due to the lack of magnetic field) decomposed into other chlorate species, to include hypochlorite (the anion in bleach and bleaching powder). The reaction of hypochlorite with the amino acids glycine and alanine, those used in the labeled release experiments, would liberate CO2.
This experiment was designed to show that the immediate release of CO2 was the result of the decomposition of chlorinated alanine, due to the chloroamine’s high decomposition rate , and the extended/prolonged evolution was due to the slower decomposition of the chloroamine of glycine.
Analytical Chemistry | Environmental Chemistry
NASA Ames Research Center (ARC)
This material is based upon work supported by the Chevron Corporation and is made possible with contributions from the National Science Foundation under Grant No. 1340110, Howard Hughes Medical Institute, S.D. Bechtel Jr. Foundation, National Marine Sanctuary Foundation, and from the host research center. Any opinions, findings, and conclusions or recommendations expressed in this material are solely those of the authors. The STAR Program is administered by the Cal Poly Center for Excellence in STEM Education on behalf of the California State University system.