BEHAVIOR OF AMINO ACIDS AND PEPTIDES EXPOSED IN EARTH ORBIT

摘要

In order to understand the chemical comportment of organic molecules of prebiotic interest when exposed to space conditions, amino acids, derivatives and peptides where exposed in Earth orbit during the CNES "Perseus-Exobiologie" mission. Dry films of samples were exposed free or associated with mineral powders to vacuum and to solar light down to 120nm during three months outside the MIR station. After the mission, the remaining products were analyzed with respect of chemical degradation, racemization and polymerization. The analyses revealed a higher sensitivity of amino acids comparatively to peptides. The identification of byproducts has allowed determining some photolysis pathways where decarboxylation and decarbonylation were found to be the major chemical reactions for amino acids and peptides, respectively. The study of associated minerals have shown that meteoritic powder was the most efficient to protect samples against UV light. The exposure of different peptides associated to meteorite powder of various thickness of have allowed to determine that 5μm films were at least necessary to protect associated organics. Implications for the exogenous origin of organics are discussed.