Determination of the Possible Source of Chlorinated Hydrocarbons Detected By SAM during MSL Mission

Thursday, 18 December 2014
Arnaud Buch1, Imene Belmahdi2, Cyril Szopa3, Caroline Freissinet4, Daniel Patrick Glavin5, Pascaline Francois6, Patrice J Coll6, Kristen Miller7, Jennifer L Eigenbrode5, Jennifer C Stern5, Rafael Navarro-Gonzalez8, Amy McAdam9, Samuel Teinturier5, jean-Yves Bonnet3, Roger E Summons10, Maeva Millan3, Tristan Dequaire6, Michel Cabane3 and Paul R Mahaffy11, (1)Organization Not Listed, Washington, DC, United States, (2)ecole centrale Paris, LGPM, Chatenay Malabry, France, (3)LATMOS Laboratoire Atmosphères, Milieux, Observations Spatiales, Paris Cedex 05, France, (4)NASA Goddard Space Flight Center, NASA Postdoctoral Program, Greenbelt, MD, United States, (5)NASA Goddard Space Flight Center, Greenbelt, MD, United States, (6)LISA, Creteil Cedex, France, (7)MIT Lincoln Laboratory, Lexington, MA, United States, (8)Universidad Nacional Autonoma de Mexico, Mexico City, Mexico, (9)NASA Goddard Space Flight Center, Planetary Environments Laboratory, Greenbelt, MD, United States, (10)Massachusetts Institute of Technology, Cambridge, MA, United States, (11)NASA Goddard SFC, Greenbelt, MD, United States
The SAM GC-MS instrument on the Curiosity rover allows to analyze volatile compounds from the atmosphere or volatile compounds from the Martian regolith and refractory compounds in the regolith after sample treatment using wet chemistry. One portion of the wet chemistry experiment is composed of MTBSTFA (N-methyl-N-tert-butyldimethylsilyltrifluoroacetamide) / DMF (dimethylformamide).

Abundant chlorinated hydrocarbons have been detected with SAM when analyzing samples collected in several sites explored by Curiosity rover. Some of these chlorohydrocarbons are produced during pyrolysis by the reaction of Martian oxychlorine compounds in the samples with terrestrial carbon from a derivatization agent (MTBSTFA) used in SAM (1, 2). Chlorobenzene cannot be formed by the direct reaction of MTBSTFA and DMF when heated in the presence of fused silica and perchlorates under SAM-like conditions (1)) therefore two other reaction pathways for chlorobenzene were proposed : (1) reactions between the volatile thermal degradation products of perchlorates (e.g. O2, Cl2 and HCl) and Tenax® and (2) the interaction of perchlorates with organic material from the martian regolith such as benzenecarboxylates (3, 4).

This study investigates several propositions for chlorinated hydrocarbon formation by looking for: (1) all products coming from the interaction of Tenax® (which is part of the SAM hydrocarbon trap) and perchlorates, (2) also between some soil sample and perchlorates in the presence or absence of MTBSTFA and (c) sources of chlorinated hydrocarbon precursors.

References: 1. D. P. Glavin et al.(2013) JGR 118, 1955–1973. 2. L. a Leshin et al. (2013) Science 341, 1238937. 3. C. Freissinet et al. (2014) LPSC XXXXV Abstract 2796. 4. D. Glavin et al. (2014) LPSC XXXV Abstract #1157.