Chloromethane release from carbonaceous meteorite affords new insight into Mars lander findings

Frank Keppler, David B. Harper, Markus Greule, Ulrich Ott, Tobias Sattler, Heinz F. Schöler, John T.G. Hamilton

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Abstract

Controversy continues as to whether chloromethane (CH3Cl) detected during pyrolysis of Martian soils by the Viking and Curiosity Mars landers is indicative of organic matter indigenous to Mars. Here we demonstrate CH3Cl release (up to 8 μg/g) during low temperature (150-400°C) pyrolysis of the carbonaceous chondrite Murchison with chloride or perchlorate as chlorine source and confirm unequivocally by stable isotope analysis the extraterrestrial origin of the methyl group (δ 2H 1800 to 11100%, δ13C219.2 to110%,). In the terrestrial environment CH3Cl released during pyrolysis of organic matter derives from the methoxyl pool. The methoxyl pool in Murchison is consistent both in magnitude (0.044%) and isotope signature (δ2H110546626%, δ 13C143.2638.8%,) with that of theCH3Cl released on pyrolysis. Thus CH3Cl emissions recorded by Mars lander experiments may be attributed to methoxyl groups in undegraded organic matter in meteoritic debris reaching the Martian surface being converted to CH3Cl with perchlorate or chloride in Martian soil. However we cannot discount emissions arising additionally from organic matter of indigenous origin. The stable isotope signatures of CH3Cl detected on Mars could potentially be utilized to determine its origin by distinguishing between terrestrial contamination, meteoritic infall and indigenous Martian sources.

Original languageEnglish
Article number7010
JournalScientific reports
Volume4
DOIs
Publication statusPublished - Nov 13 2014

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Keppler, F., Harper, D. B., Greule, M., Ott, U., Sattler, T., Schöler, H. F., & Hamilton, J. T. G. (2014). Chloromethane release from carbonaceous meteorite affords new insight into Mars lander findings. Scientific reports, 4, [7010]. https://doi.org/10.1038/srep07010