Fluid dynamics and orbital constraints on Mars’ thermal and rheological evolution.

While the present-day surface of Mars is relatively well documented and characterized, the details of its internal structure and its evolution remain, in comparison, poorly known. The interpretation of space mission data by means of geophysical and geodynamic considerations allows the thermal evolution of Mars silicate and metallic envelopes to be constrained. However, the limited amount of available data, and the interplay between several physical quantities (e.g., temperature, composition, and rheology) require strong assumptions to be made about the values of several key parameters in order to infer the Martian thermal history. The InSight mission is expected to significantly improve our knowledge of the interior of Mars, in particular via seismic recordings and heat flux measurements. The mission will also attempt to refine previous estimates of Mars’ Love number, which influences the orbital evolution of its satellites, Phobos and Deimos. The main difference between these two objects is that the first one is spiraling towards the planet, while the second, located beyond the synchronous orbit, is progressively moving away from it. These orbital changes are also governed by Mars' tidal dissipation. Similar to the thermally activated process of seismic wave attenuation in planetary bodies, tidal dissipation is related to the thermal state of the planets. During the first part of my presentation I will show how one can further constrain the thermal and rheological histories of Mars by exploiting the link between tidal attenuation and thermal state. In a second part, I will present simple fluid dynamics numerical experiments designed to characterize the relationships between the rheology of Mars’ mantle, and the thickness of its crust. Such constraints provide additional and alternative ways to decipher the dynamic history of Mars, and would improve the interpretation of upcoming data.