Determination of the Possible Sources of Chlorinated Hydrocarbons Detected During Viking and MSL Missions

Abstract : Interest of exploration on Mars Mars is interesting given that its early history is similar to one on the Earth. In fact, volcanoes were still active, the environment was wetter and warmer and the magneto-sphere still existed. Source of organic Mars: Various sources of endoge-nous organic matter (OM) could have existed including (a) abiotic production via hydrothermal vents, volcanism and atmospheric synthesis and (b) biotic synthesis. Currently, the sources of extraterrestrial organic compounds that should be delivered to Mars are known: carbon-rich meteorites , micrometeorites, comets and interstellar dust particles. Stabilization of the OM takes place through three mechanisms described in the article of Lützow (1): (1) First, the selective preservation of OM is described as a phenomenon of accumulation of some compounds because of their resistance against the environment. (2) The second path which allows the persistence of OM is the space isolation of OM from environmental stress. (3) The last way to stabilize the OM is intermolecular interactions between minerals or metal ions with OM. One of the primary objectives of the Mars Science Laboratory (MSL) mission is to search for environments on the Martian surface that have preserved OM. Structure and aim of SAM Sample Analysis at Mars (SAM) is one of the instruments of the MSL mission. Three analytical devices are onboard SAM: the Tunable Laser Spectrometer (TLS), the Gas Chromatograph (GC) and the Mass Spectrometer (MS) (2). Solid sample preparation: To adapt the nature of a sample to the analytical devices used, a sample preparation and gas processing system implemented with (a) a pyrolysis system, (b) wet chemistry: MTBSTFA and TMAH (c) the hydrocarbon trap (silica beads, Tenax® TA and Car-bosieve G) which is employed to concentrate volatiles released from the sample prior to the GC-MS analyses. Detection of chlorinated hydrocarbons All chlorinated hydrocarbons detected during the Viking I and II missions and MSL (Rocknest (RN), John Klein (JK), Cumberland (CB) and Confidence Hill (CH)) are listed in Table 1. Viking landers (1976): The origin of chloromethane and dichloromethane was explained at the time by terrestrial contamination from the instruments (3). In a recent paper from Navarro-González (4), these results have been rein-terpreted and chlorinated compounds could have been the product of the reaction of perchlorates identified by Phoe-nix (5) with martian organic carbon present in the sample or terrestrial organic carbon in the instrument or sample handling chain. MSL (2011): A diverse range of chlorinated hydrocarbons have been detected with SAM after GCMS analysis of samples collected from several sites explored by Curiosity rover (Table 1). 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) present in SAM (6, 7). Chlorobenzene (CBZ) cannot be formed by the reaction of MTBSTFA and perchlorates (6) and two other reaction pathways for CBZ were therefore 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 (T > 200 °C) with OM from Mars's soil such as benzenecarbox-ylates (8, 9). Among all the sample analyzed by SAM, JK and CB sites are interesting; smectites (phyllosilicates-18 to 22 wt %) and quartz (0.1 to 1 wt %) were detected at the two sites (10) and could have an important role in the preservation of OM (1). Objectives This study investigates several hypotheses for chlorin-ated hydrocarbon formation by looking for: (a) all products coming from the interaction of Tenax® and perchlorates, (b) products between various soil sample and perchlorates and (c) sources of chlorinated hydrocarbon precursors. Experiments and methods: To answer some of our remaining questions, laboratory experiments were done in several solid matrices which Viking MSL RN JK CB CH
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A. Buch, Imène Belmahdi, Cyril Szopa, Caroline Freissinet, Daniel Glavin, et al.. Determination of the Possible Sources of Chlorinated Hydrocarbons Detected During Viking and MSL Missions. 46th LPSC Lunar and Planetary Science Conference, Mar 2015, Houston, United States. ⟨hal-01815527⟩

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