Evidence of martian perchlorate, chlorate, and nitrate in Mars meteorite EETA79001: Implications for oxidants and organics

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2014-02, Vol.229, p.206-213
• Main Authors: Kounaves, Samuel P., Carrier, Brandi L., O’Neil, Glen D., Stroble, Shannon T., Claire, Mark W.
• Format: Article
• Language: English
• Subjects: Astrobiology; Contamination; Inclusions; Mars; Mars, surface; Meteorites; Oxidants; Oxidation; Regoliths; Sawdust; Soil (material)
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2013.11.012

•Analyses of martian meteorite EETA79001 show presence of ClO4-, ClO3-, and NO3-.•ClO4- concentration too high to be accounted for by accumulation during 12kyr residence on Earth.•Quantity and location within EETA79001 suggests martian origin.•Similarity of the δ15N for the EETA79001 to Tissint also suggests martian in origin.•Presence of ClO3- is an indicator that oxychlorines are present in the martian soil. The results from the Viking mission in the mid 1970s provided evidence that the martian surface contained oxidants responsible for destroying organic compounds. In 2008 the Phoenix Wet Chemistry Lab (WCL) found perchlorate (ClO4-) in three soil samples at concentrations from 0.5 to 0.7wt%. The detection of chloromethane (CH3Cl) and dichloromethane (CH2Cl2) by the Viking pyrolysis gas chromatograph–mass spectrometer (GC–MS) may have been a result of ClO4- at that site oxidizing either terrestrial organic contaminates or, if present, indigenous organics. Recently, the Sample Analysis at Mars (SAM) instrument on the Mars Science Laboratory (MSL) Curiosity directly measured the presence of CH3Cl, CH2Cl2 and, along with measurements of HCl and oxygen, indirectly indicate the presence of ClO4-. However, except for Phoenix, no other direct measurement of the ClO4- anion in martian soil or rock has been made. We report here ion chromatographic (IC) and isotopic analyses of a unique sawdust portion of the martian meteorite EETA79001 that show the presence by mass of 0.6±0.1ppm ClO4-, 1.4±0.1ppm ClO3-, and 16±0.2ppm NO3- at a quantity and location within the meteorite that is difficult to reconcile with terrestrial contamination. The sawdust sample consists of basaltic material with a minor salt-rich inclusion in a mass ratio of ∼300:1, thus the salts may be 300 times more concentrated within the inclusion than the whole sample. The molar ratios of NO3-:ClO4- and Cl-:ClO4-, are very different for EETA79001 at ∼40:1 and 15:1, respectively, than the Antarctic soils and ice near where the meteorite was recovered at ∼10,000:1 and 5000:1, respectively. In addition, the isotope ratios for EETA79001 with δ15N=−10.48±0.32‰ and δ18O=+51.61±0.74‰ are significantly different from that of the nearby Miller Range blue ice with δ15N=+102.80±0.14‰ and δ18O=+43.11±0.64‰. This difference is notable, because if the meteorite had been contaminated with nitrate from the blue ice, the δ15N values should be the same. More importantly, the δ15N is similar to the uncontaminated Tissi