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Communication Dans Un Congrès Année : 2018

Evolution of organic molecules under Mars surface-like UV radiation conditions simulated in space and laboratory

Résumé

The detection and identification of organic molecules at Mars are of primary importance for astrobiology, as some of these molecules are life precursors and components. While in situ exploration missions are searching for them at the surface of the planet, it is essential to understand how organic molecules evolve and are preserved at the surface of Mars. Indeed the harsh conditions of the environment of Mars, such as ultraviolet (UV) radiation or oxidative processes, due for example to iron-bearing minerals and perchlorate ions, could explain the low abundance and diversity of organic molecules detected so far [1][2]. In order to get a better understanding of the evolution of organic matter at the surface of Mars, we exposed organic molecules under Mars-like UV radiation and oxidative environments. Similar organic samples were exposed in two experiments: directly to the Sun radiation, outside the International Space Station (ISS) on the EXPOSE R2 facility; and under the flux of a wide range UV lamp in the laboratory with the MOMIE experiment. The EXPOSE R2 facility was placed in low Earth orbit (LEO), outside the International Space Station (ISS) in 2014, to be exposed to the Solar radiation. One of the EXPOSE R2 experiment, called PSS (Photochemistry on the Space Station), was dedicated to astrobiology- and astrochemistry-related studies. Several of the PSS samples were prepared for the study of the evolution of organic molecules under Mars-like surface radiation conditions. Organic samples have been exposed directly to the Sun under KBr filters (UV transmission >200 nm) from November 2014 to February 2016, mimicking the UV radiation conditions of the surface of Mars. Four types of samples were exposed in the form of thin layers of solid molecules: pure deposits of adenine, adenine mixed with nontronite (a clay mineral detected on Mars), pure deposits of chrysene and glycine mixed with nontronite.The MOMIE (Mars Organic Matter Irradiation and Evolution) experiment has been set up to study the evolution of organic matter under simulated martian UV radiation within the laboratory [3][4]. Organic samples are in this case exposed under a UV lamp (200-400 nm) as thin homogenous films (a fraction of μm thick). Adenine, chrysene and glycine were studied in this experiment as well, allowing us to compare their evolution with the results in LEO. Uracil was also studied. Perchlorate salts effect on organic evolution was investigated. To characterize the evolution of our samples, analyses by infrared spectroscopy (IRTF) were performed: before and after exposure in LEO, for the PSS samples, and continuously along the experiment for the MOMIE samples. These analyses allowed determining whether each molecule is preserved or photodegraded, and if so, its photolysis rate. Most of the studied molecules were rapidly degraded under Mars-like UV radiation. On the other hand, uracil seems to form new bigger compounds in Mars-like UV radiation conditions. The effect of nontronite and perchlorates on organic molecules preservation has been investigated as well. We also compared results from LEO with laboratory data.
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insu-04434577 , version 1 (02-02-2024)

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Laura Rouquette, Didier Chaput, Patrice Coll, Herve Cottin, Fabien Stalport, et al.. Evolution of organic molecules under Mars surface-like UV radiation conditions simulated in space and laboratory. 42nd COSPAR Scientific Assembly, Jul 2018, Pasadena, United States. pp.Abstract id. F3.1-10-18. ⟨insu-04434577⟩
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