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Evolution de molécules organiques en conditions martiennes simulées : expériences en laboratoire et en orbite basse terrestre sur la Station Spatiale Internationale

Abstract : Organic molecule detection at Mars is one of the main goals of the current and future Mars exploration space missions, Mars Science Laboratory (MSL, NASA) and ExoMars 2020 (ESA). Several organic sources exist : abiotic sources (interplantary medium, hydrothermalism and atmospheric synthesis) but also biotic sources such as potential past biological activity. Curiosity from the MSL mission detected chlorinated and sulfur organic compounds. However these compounds can not be linked to any biological activity and do not represent the meteoritical organic diversity.The main hypothesis to explain the low diversity of detected organic compounds at Mars is that the martian environment degrade organic matter. In order to understand organic molecule evolution at the Martian surface and be able to guide and help interpret in situ analysis, I worked on two experimental simulations mimicking some of the martian environmental conditions (UV radiation, pressure, temperature and mineral composition). MOMIE, for Mars Organic Matter Irradiation at Mars, is a laboratory experiment set up at the LISA laboratory (Créteil, France). PSS, for Photochemistry on the Space Station, has been set up on the International Space Station (ISS) in low Earth orbit, using directly filtered UV photons from the Sun.I studied the evolution of four organic molecules likely to be present at Mars with ou without a mineral phase : glycine (an amino acid), adenine and uracil (two nucleobases), and chrysene (a polycyclic aromatic hydrocarbon). Glycine, adenine and chrysene are degraded at Mars surface with quantum efficiencies of photodecomposition from 6,4 ± 1,4 x 10-6 to 2,3 ± 1,0 x 10-3 molecule.photon-1. Uracil evolve into more stable photoproducts with a production efficiency of 1,64 ± 1,43 x 10-1 molécule.photon-1. Four uracil dimers have been identified as uracil photoproducts. Finally, the studied mineral phases, an amorphous iron-rich phase and perchlorates, accelerate organics evolution or degradation
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Laura Rouquette. Evolution de molécules organiques en conditions martiennes simulées : expériences en laboratoire et en orbite basse terrestre sur la Station Spatiale Internationale. Ingénierie de l'environnement. Université Paris-Est, 2018. Français. ⟨NNT : 2018PESC1096⟩. ⟨tel-02083961⟩

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