Insolation-driven variations of Mercury's crustal thickness

Kurzfassung

Gravity and topography data are traditionally interpreted in terms of undulations of the crust-mantle interface across which a density jump occurs. The analysis of MESSENGER data suggests the existence of significant large-scale variations in the crustal thickness of Mercury. In particular, models that use the mineralogy of the surface to guide the choice of the crustal density predict that the so-called high-Mg region is underlain by a thick crustal root resulting from a high-degree of partial melting. Standard numerical simulations using a constant surface temperature predict that convection in Mercury's thin mantle is characterised by a laterally-uniform pattern of small-scale up- and downwellings with nearly unitary aspect ratio. While the overall amount of crust produced in such models compares favourably with estimates of the mean crustal thickness, the lateral distribution of crust reflects the convection pattern and is thus difficult to reconcile with the large-scale variations inferred from the remote-sensing data. Lateral variations in surface temperature due to uneven insolation can induce long-wavelength variations of the mantle temperature at depth and in turn, affect the generation of partial melt. By using 3D simulations of the thermo-chemical evolution of Mercury, we investigate the influence of insolation on the production of Mercury's crust with the goal of generating large-scale variations comparable with those predicted by gravity and topography data. Besides key parameters controlling convection such as the mantle viscosity and amount of internal heating, we test the influence of the insolation associated with the present-day 3:2 resonance and with a putative 1:1 resonance that may have characterised the early evolution of Mercury.