Mars Organic Matter Revealed by the Detection of Organo-chlorinated Molecules from Pyro-GCMS Analyses of Yellowknife Bay Mudstone

International audienceMudstones collected on the Yellowknife Bay site in Gale crater by the Curiosity rover, were analyzed with the Sample Analysis at Mars (SAM) chemical laboratory with the aim (among others) to detect and identify organic molecules in the Martian reglith [1]. The pyrolysis (to 900°C)-gas chromatography-mass spectrometry (Pyro-GCMS) analytical mode was systematically used to reach that goal. It revealed the existence of complex interactions between compounds present in the soil sample (e.g. oxychlorines [2]) and internal components of the SAM experiment (e.g. derivatization reactant) resulting in signals complex to interpret [3].By comparing these results with those obtained for the other Mars samples analysed with SAM, and by carefully identifying, from laboratory work, the possible SAM internal contributions to the organic molecules detected [4], chlorobenzene has already been identified as mainly originating from organics present in the mudstone [5]. Since this discovery, we did additional studies of the chromatograms that reveal the presence of dichlorobenzene originating from an organic source endogenous to the sample. Even if the exact original source of these organic molecules cannot be strictly identified, the detection of several chlorinated aromatic molecules suggests the presence of a significant amount of aromatized materials which are in an oxidized state involving oxygen in the mudstone. We present here the corresponding results and the implication it can have on the origin of these organic materials.References: [1] Mahaffy, P. et al. (2012) Space Sci Rev, 170, 401-478. [2] Glavin, D. et al. (2013), JGR. [3] Ming D. et al. (2013), Science 32, 64, [4] Miller K. et al. (In press), JGR, [5] Freissinet et al., (2015), JGR Pla. 120, 495

Preservation of organic matter on Mars by sulfur

International audienceDeltaic-lacustrine mudstones at Pahrump Hills, Gale Crater, Mars yielded a variety of sulfur-containing volatiles upon heating to 500-860°C, as detected by the Sample Analysis at Mars (SAM) instrument onboard the Curiosity rover. The detection of organosulfur compounds comprising thiophenes, dimethylsulfide and thiols by gas chromatography-mass spectrometry and evolved gas analyses, together with aromatic and other hydrocarbon molecules with distributions specific to the sample (i.e., not from the SAM background) indicate that some or all of these organic fragments released at high temperatures are indigenous to the mudstones. The organosulfur compounds are most likely derived from sulfur organics in the sediments. However, there is a possibility that sulfurization of some organic fragments occurred in the oven. On Earth, sulfurization of organic matter is a key process that aids preservation over geological time-scales. This is because it reduces reactive functional groups and adds cross links between small unstable molecules thereby converting them into recalcitrant macromolecules. Sulfurization of organic materials prior to deposition and during early diagenesis may have been a key mechanism responsible for organic matter preservation in the Murray formation mudstones. Sulfur-bearing organics have also been observed in carbonaceous meteorites and there is indication of their presence in the Tissint martian meteorite. A quantitative assessment of organosulfur compounds relative to their non-organic counterparts will be presented for the Murray formation mudstones analyzed by SAM and meteorites analyzed in the laboratory under similar analytical conditions

From SAM Instrument Background to Martian Signal: Challenges of Solid Sample Analyses on Mars

International audienceTaken together, these results indicatethat the internal SAM sources createa background that challengesthe analysis of solid samplesin search for organics, creating interferences between terrestrial andpossible indigenous carbon sources. We have been exploring the possibility of SAM-derived C contributions to chlorohydrocarbon generation. Current observations provide no direct link between SAM internal sourcesand the chlorohydrocarbons detected on Mars, thus a martian organic contribution to the chloromethanes, dichloroalkanes and chlorobenzene detected at CBis possible

Role of the Tenax® adsorbent in the interpretation of the EGA and GC‐MS analyses performed with the Sample Analysis at Mars in Gale crater

International audienceThe Sample Analysis at Mars (SAM) experiment on the NASA Curiosity rover seeks evidence of organic compounds on the surface of Mars. Since the beginning of the mission, various organic molecules have been detected and identified. While several have been demonstrated to be indigenous to the Martian soil and rocks analyzed, others appear to have been produced from sources internal to the experiment.The objective of this study is to build an exhaustive molecular database to support the interpretation of SAM results by identifying all the chemical species produced from Tenax® adsorbents, by determining: (1) the thermal degradation byproducts of Tenax®, (2) the effect of Tenax® conditioning on the formation of Tenax® byproducts, (3) the impact of MTBSTFA or a mixture of MTBSTFA and DMF on Tenax® decomposition, and (4) the reaction between Tenax® and calcium perchlorate.Our results indicate that the by‐products of the SAM trap are due to the impact of trap heating, the impact of the derivatization reagent (MTBSTFA) and the presence of perchlorate in Martian soil. Some of these by‐products are observed in the SAM gas chromatograph mass spectrometer (GCMS) data from Mars

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

International audienceInterest 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 C