Influence of Oxychlorine Phases on the Pyrolysis of Organics Trapped in Jarosite and the Quest of Organics on Mars with the SAM Instrument Onboard Curiosity

The Curiosity rover is currently analyzing the base of Mt Sharp in Mars' Gale crater to find clues of habitability in the stratigraphic layers of rocks. One of its goal is the search of organic compounds thanks to the Sample Analysis at Mars (SAM) experiment. With this aim, SAM performs in situ molecular analysis of gases evolved from the heat of the solid samples collected by Curiosity. SAM uses a gas-chromatograph mass-spectrometer (GCMS), to detect/identify inorganics and organics present in the samples. During the pyrolysis, chemical reactions can occur between the gases thermally released from minerals and organic molecules SAM is looking for. Beyond the minerals involved, oxychlorines, likely spread at Mars' surface, liberate dioxygen and chlorine species, and sulfates release sulfur-bearing species. The detection of Cl- and S-bearing organics were attributed to reactions between oxychlorines, sulfates and organics. These last were proved to come from SAM instrument background and Mars indigenous organics, proving the presence of organics on Mars. However, the identification of their precursors is complex due to the chemical reactivity in the SAM ovens. Recent studies suggest compounds from various chemical families, as potential precursors of the chlorohydrocarbons detected on Mars, but considered limited parameters and mineralogy. Laboratory experiments have been performed to understand the influence of oxychlorines on organic matter incorporated in sulfates, during pyrolysis. To do so, organics from chemical families potentially present on Mars and synthetized in laboratory within jarosite, a ferric sulfate, were pyrolyzed in presence of oxychlorines. GCMS was used to identify the pyrolysis products and try to correlate them with the organo-chlorinated compounds detected by SAM. This helps discriminate their likely parent organics or chemical families. The work includes the investigation of sulfurized compounds generated from reactions between the organics, including the wet chemistry reagent (MTBSTFA) known to be present in SAM background, and the S-bearing inorganic species released from the Jarosite. The results and conclusions about the SAM measurements will support the analysis and interpretation of the future analyses to be done by the MOMA-GCMS experiment of the Exomars 2020 mission.