Influence of the secondary X-Rays on the organic matter at Mars’ near-surface
Résumé
In 2015 the SAM experiment on board the curiosity rover discovered the first organic molecule endogenous to Mars. This molecule is certainly the result of the reaction of a still unknown molecule with the perchlorates/chlorates present in the Martian soil [1]. Since then, other organics have been discovered: sulfur and nitrogen bearing molecules [2-3] and chlorohydrocarbons [4]. Those chlorohydrocarbons compounds could be generated by a reaction which 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 [5], 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 (hard and soft X-ray) on various organic molecules, the chiral amino acids L-alanine and L-phenylalanine and two potential precursors of chlorobenzene, benzoic and trimesic acids. These molecules were irradiated pure but also in contact with calcium perchlorate in order to better understand the roles in perchlorates present in the Martian soil. We also studied the molecules within mineral matrices in the form of pellets, in absence and in presence of perchlorates (max 3 % weight).