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P. Coll, F. Stalport (LISA - FRANCE), M. Cabane (SA - FRANCE), R. Navarro-Gonzalez (LQPEP - UNAM - MEXICO), A. Person (LGS - FRANCE), F. Raulin (LISA - FRANCE)
Many observations of Mars confirm the presence of liquid water running out freely on its surface and a dense atmosphere (20-30bars) made up primarily of CO2 in the first million years after formation. Such conditions were met for Earth, allowing the development of Life. Consequently a form of Martian Life could also have appeared. But Mars thereafter did not follow the same evolution as Earth: the only water traces currently observed are in solid or gas forms and the main atmosphere disappeared (6hPa). What happened to CO2 on Mars? The presence, at beginning, of liquid water undoubtedly allowed as on Earth the formation of inorganic and maybe organic carbonates, supposing that a form of carboneous Life appeared over Mars as on Earth. The absence of tectonics and volcanicity on Mars would not have counterbalanced the loss of atmospheric CO2. This description of past Life on Mars requires to lay out of databases of terrestrial-biomineral characteristics used as Martian-analogues. Within this framework, we studied the thermal behevior of carbonate samples (calcite, aragonite...) of biotic and abiotic origin in order to highlight specificities of materials of biological origin. We used samples collected allover the world (present and fossil carbonates of shells, corals, stromatolites, microbialites, samples from extreme environments...). Materials have been analysed by TDA-TG to determine and compare profiles of mass loss in CO2 according to temperature. Measurements by X-ray diffraction and by Pyr-GC-MS have been carried out, isotopic ratios of O and C complete these characterizations. These results are of primary importance to propose an original method of in situ detection of a biotic activity over Mars (for example in the frame of the SAM suite of instruments proposed on MSL09) and for laboratory analysis in case of Martian Sample Return. This work has been supported by CNES grants since 2002.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.