Understanding the Influence of the Secondary X-Rays on the Organic Matter at Mars' Near-Surface with the Soleil Synchrotron Beam Line LUCIA
Résumé
The SAM instrument onboard NASA Curiosity rover revealed organic matter indigenous to Mars samples through the detection of chlorohydrocarbons, and sulfur and nitrogen bearing molecules. Chlorohydrocarbons are thought to mainly originate from a reaction of unidentified higher molecular mass organic compounds with perchlorates and chlorates present in the soil. The reaction may occur at Mars' near-surface induced by the harsh radiative environment, e.g. direct radiation (UV, 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 lower concentration than expected from modelling, suggesting organic matter degradation over geological time. Our team thus investigates the influence of radiations on organic molecules under simulated Mars' surface conditions. In the present study, we mainly focused on the action of X-rays on four organic molecules, the chiral amino acids L-alanine and L-phenylalanine and two potential precursors of chlorobenzene (one of the chlorohydrocarbons detected by SAM), benzoic and trimesic acids. Those pure molecules deposits are produced by sublimation on an optical window or mixed with perchlorate. We also studied the molecules within mineral matrices in the form of pellets, in absence and in presence of perchlorates.