Characterization of the organic matter in the comet 67P/Churyumov-Gerasimenko

Comets are among the richest body in organic matter of Solar System. The remote sensing observations have already identified more than two dozen of simple organic molecules in the gas phase. Moreover, in situ exploration missions (Giotto, Vega-1 and Vega-2), as well as the sample return of the Stardust mission, have established that in addition to these relatively simple volatile molecules, a significant fraction of cometary carbonaceous material remain solid in the cometary grains. COSIMA (Cometary Secondary Ion Mass Analyzer) is a time of flight - secondary ion mass spectrometer on board the orbiter of the Rosetta mission. LISA and LPC2E participate to the definition of the operations and to the interpretation of the observations of this instrument. Recent observations performed with this instrument can confirm the presence of solid organic matter in the cometary grains. While the interpretations of these findings are still preliminary, it appears that the chemical structure of this organic matter is not the one that we were expecting. Thus, we lack of representative reference spectra. However, we suspect that the cometary organic material has been strongly heated and / or irradiated before the accretion of the cometary nucleus. The aim of the thesis is to describe as accurately as possible the organic matter observed thank to the COSIMA instrument. New synthesis of complex organic material synthesis will be performed in our laboratory (LISA) thank to the experimental setup named 'OREGOC' (French acronym for Origin and Evolution of Ices and Cometary Organic matter) that allows ultraviolet photolysis and heating ice mixtures. We will particularly insist on a higher energy deposition during the photolysis that what we have achieved in the past. Once produced, these samples will be analyzed using the two 'ground' instruments of COSIMA: the first being located at LPC2E Orleans and the second at the Max Planck Institute in Goettingen, Germany. The aim is naturally to reproduce the observations made on the grains of the comet 67P / Churyumov-Gerasimenko thank to synthetic samples to clarify the nature of the cometary organic matter and its chemical evolution since its synthesis to its ejection from the cometary nucleus. (author)