Methane clathrate hydrate stability in the martian subsurface and outgassing scenarios

Methane on Mars continues to be the subject of much debate, particularly because its generation mechanism remains unidentified. Regardless of its formation, methane could be stored in subsurface reservoirs such as clathrate hydrates. Their destabilization stimulated by pressure and temperature changes could be the source of the recent observations of martian methane. In this thesis work, a subsurface thermal model is first coupled with a thermodynamic model of clathrate hydrates in order to define global stability regions in the martian crust and to investigate methane trapping. Then, a diffusive-adsorptive model of gas transport is used to constrain the intensity, variation and duration of the surface flux resulting from shallow CH4 sources located into the stability zone of clathrate hydrates on Mars. Finally, atmospheric transport simulations based on these surface flux patterns are compared to observations. Our results show that stability conditions of methane clathrate hydrate are already met in the shallow martian subsurface (a few meters to a few tens of meters deep). However, clathrates that would form at depth in the martian crust would contain a larger fraction of methane than shallow clathrates formed from a similar gas phase. While diffusive transport is consistent with low background levels of methane measured at Gale crater, clathrate dissociation and subsequent methane diffusion through the regolith cannot be responsible for CH4 spikes or short-live methane plumes.