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

• Published in: Scientific reports 2014-11, Vol.4 (1), p.7010-7010, Article 7010
• Main Authors: Keppler, Frank, Harper, David B., Greule, Markus, Ott, Ulrich, Sattler, Tobias, Schöler, Heinz F., Hamilton, John T. G.
• Format: Article
• Language: English
• Subjects: 704/445/209; 704/445/849; Chlorides; Chlorine; Chloromethane; Contamination; Emissions; Humanities and Social Sciences; Low temperature; Mars; multidisciplinary; Organic matter; Perchlorate; Perchloric acid; Pyrolysis; Science; Stable isotopes; Temperature effects; Terrestrial environments
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/srep07010

Controversy continues as to whether chloromethane (CH 3 Cl) detected during pyrolysis of Martian soils by the Viking and Curiosity Mars landers is indicative of organic matter indigenous to Mars. Here we demonstrate CH 3 Cl 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 2 H +800 to +1100‰, δ 13 C −19.2 to +10‰,). In the terrestrial environment CH 3 Cl 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 (δ 2 H +1054 ± 626‰, δ 13 C +43.2 ± 38.8‰,) with that of the CH 3 Cl released on pyrolysis. Thus CH 3 Cl 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 CH 3 Cl 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 CH 3 Cl detected on Mars could potentially be utilized to determine its origin by distinguishing between terrestrial contamination, meteoritic infall and indigenous Martian sources.