Caractérisation des processus d'altération à la surface de Mars primitive par approche expérimentale et télédétection

摘要

The geologic record of Mars has preserved some minerals indicating that aqueous alteration occurred during several hundreds of million years after the formation of the planet. The reconstruction of these ancient processes is a major stake of planetary sciences, since the evolution of early Earth is now inaccessible due to the recycling of the terrestrial crust by plate tectonics, volcanism and erosion. This thesis brings several contributions to the understanding of alteration processes on early Mars through alteration experiments under carbon dioxide and through the analysis of visible-and-near-infrared data acquired from orbit. The results lead to a model involving the combined alteration of silicates and iron sulfides to explain the formation of the Martian sulfates, which proved consistent with the limited spatial and temporal extension of sulfates. Consistently, the study of secondary minerals in the Ismenius Cavus depression illustrates that the acidic alteration from which sulfates derive has not affected the entire planet. A second orbital study focused on the western plateau of Nili Fossae shows that at least part of Martian clays has derived from weathering. This conclusion is supported by an experimental alteration of olivine in simulated Martian conditions confirming that the minerals observed in Nili Fossae and other regions of Mars are compatible with an alteration under a carbon dioxide atmosphere denser than today, which would have ensured the stability of liquid water on the surface of the planet.