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Communication Dans Un Congrès Année : 2021

Impact of secondary X-Rays on the possible precursors of chlorinated organic compounds detected at the Mars surface (MarsOrganiX)

Résumé

The Sample Analysis at Mars (SAM) instrument onboard NASA Curiosity rover revealed for the first time, organic matter indigenous to a Martian sample with the detection of chlorohydrocarbons [1]. These molecules are thought to originate from a reaction of unidentified higher molecular mass organic matter with Martian perchlorates in the pyrolytic oven of the instrument. However, other reactions may occur at Mars' near-surface induced by the harsh radiative environment, e.g. direct radiation (UV light, high energy X- and γ-rays) and secondary photons produced by the interaction of direct radiations with the Martian regolith (low energy secondary X-rays). Additionally, organic molecules are detected in a lower concentration than expected from modelling [2], suggesting organic matter degradation over geological time. This degradation could be induced by the radiation at the Mars surface. For these reasons, we investigate the influence of radiations on organic molecules (L-Alanine, Benzoic, phthalic acid with or without presence of perchlorates) under simulated Mars' surface conditions at the laboratory. To address the influence of high energy X-rays directly reaching Mars surface on the degradation of organic molecules, a synchrotron session was undertaken on the PSICHE beam line in October 2017 (Gif sur Yvette, France). The reactivity and chemical characterization of L-alanine and benzoic acid exposed to hard X-rays (25-50 keV) did not show any degradation, up to 8 hours of irradiation, of organics nor formation of chlorohydrocarbons. The X-rays of the PSICHE beam line may have been too energetic for degrading efficiently organic molecules [3, 4]. For that reason, a new set of experiments have been done on the LUCIA beamline which combines both low energy X-rays and high photon flux, allowing to simulate processes at the geological-timescale of Mars. The use of this line also permits to follow the evolution of the samples in real time using XANES/EXAFS techniques. To follow the evolution of our samples, we used infrared spectroscopy and gas chromatography coupled to mass spectrometry analytical techniques. The energetic range provided by the monochromatic beam of LUCIA has been used to simulate the secondary fluorescence from the major elements present in the Martian near-surface, for up to a simulated 80 million years of irradiation time on Mars
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Dates et versions

insu-04471742 , version 1 (21-02-2024)

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Arnaud Buch, Fabien Stalport, Jean-Yves Bonnet, Caroline Freissinet, David Coscia, et al.. Impact of secondary X-Rays on the possible precursors of chlorinated organic compounds detected at the Mars surface (MarsOrganiX). 43rd COSPAR Scientific Assembly, Jan 2021, Sydney, Australia. pp.id.377. ⟨insu-04471742⟩
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