Evidence of martian perchlorate, chlorate, and nitrate in Mars meteorite EETA79001: Implications for oxidants and organics
文摘
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 in three soil samples at concentrations from 0.5 to 0.7 wt%. The detection of chloromethane (CH3Cl) and dichloromethane (CH2Cl2) by the Viking pyrolysis gas chromatograph-mass spectrometer (GC-MS) may have been a result of 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 . However, except for Phoenix, no other direct measurement of the 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 卤 0.1 ppm , 1.4 卤 0.1 ppm , and 16 卤 0.2 ppm 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 鈭?00:1, thus the salts may be 300 times more concentrated within the inclusion than the whole sample. The molar ratios of and , are very different for EETA79001 at 鈭?0:1 and 15:1, respectively, than the Antarctic soils and ice near where the meteorite was recovered at 鈭?0,000:1 and 5000:1, respectively. In addition, the isotope ratios for EETA79001 with 未15N = 鈭?0.48 卤 0.32鈥?and 未18O = +51.61 卤 0.74鈥?are significantly different from that of the nearby Miller Range blue ice with 未15N = +102.80 卤 0.14鈥?and 未18O = +43.11 卤 0.64鈥? This difference is notable, because if the meteorite had been contaminated with nitrate from the blue ice, the 未15N values should be the same. More importantly, the 未15N is similar to the uncontaminated Tissint Mars meteorite with 未15N = 鈭?.5鈥? These findings suggest a martian origin of the , and in EETA79001, and in conjunction with previous discoveries, support the hypothesis that they are present and ubiquitous on Mars. The presence of in EETA79001 suggests the accompanying presence of other highly oxidizing oxychlorines such as or ClO鈭?/sup>, produced both by UV oxidation of Cl鈭?/sup> and 纬- and X-ray radiolysis of . Since such intermediary species may contribute to oxidization of organic compounds, only highly refractory and/or well-protected organics are likely to survive. The global presence of , , and , has broad implications for the planet-wide water cycle, formation of brines, human habitability, organics, and life.
