SAM and the organic matter in Gale Crater, Mars - Inventory and implications

Abstract : The sample analysis at Mars (SAM) instrument onboard Curiosity rover is devoted to the search for organic molecules on Mars, which can provide important first clues of extinct or extant biota on the planet. We've identified molecules at various locations in Gale crater in the form of, 1) simple organic molecules released from pyrolyzed samples rich in clays and sulfates; chlorobenzene and dichloroalkanes were first identified in a mudstone, followed by the detection of at least two isomers of dichlorobenzene through a directed search. The pyrolysis of a drilled sample further down Curiosity's path led to the identification of S-bearing compounds such as thiophene and dimethylsulfide. The exact nature of the precursors and the origin of the low-temperature Cl-bearing and high temperature S-bearing molecules remain unclear. 2) More complex organic molecules with the use of derivatization. Two derivatization protocols were applied to SAM; a) an "opportunistic derivatization" that used the leak present in the system, and during which we can minimize interferences with perchlorates by removing O2/HCl before the reaction, and b) a full-cup derivatization, in which a cup containing the reagent was punctured. Both experiments led to complementary results, consistent with the presence of organic matter with a wider diversity than previously recognized. 3) High CO2 release at temperatures compatible with oxidation of organics, either from instrumental background or from the martian sample. However, the identification of any specific molecules remains difficult. Hundreds of parts per million of organics are estimated in the case that all of the CO2 comes from organic carbon decomposition. The detection of reduced organic compounds in martian near surface samples is a significant step towards understanding the presence, diversity and preservation of prebiotic or biotic molecular signatures on Mars. Lessons learned from the detection of organic molecules with SAM will feed forward to the planning of future experiments on this instrument and the next generation missions to Mars. It also enables a better understanding of the organics preservation potential of Mars samples in context, and therefore increases our ability to select future landing sites in the search for traces of life, and to wisely target samples to be returned.
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Submitted on : Wednesday, March 6, 2019 - 2:17:28 PM
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Caroline Freissinet, Daniel P. Glavin, Cyril Szopa, Arnaud Buch, Jennifer L. Eigenbrode, et al.. SAM and the organic matter in Gale Crater, Mars - Inventory and implications. American Geophysical Union, Fall Meeting 2018, Dec 2018, Washington, United States. pp.abstract #P13A-03. ⟨insu-02059202⟩

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