Forming Mercury by a grazing giant collision involving similar mass bodies

Abstract

Abstract The planet Mercury is predominantly made up of an iron core, covered by a comparatively thin silicate layer, which has led to the idea that this configuration is the product of mantle stripping by a giant impact. In the literature, a classical hit-and-run impact has been explored in which a roughly Mars-mass proto-Mercury collides with an Earth-mass target, losing large parts of its mantle. However, such hit-and-run collisions between proto-planets of very different masses are rare in N-body simulations of terrestrial planet formation. On the other hand, hit-and-run collisions involving similar mass bodies appear to be more frequent. Our aim here is to investigate the conditions under which collisions of similar mass bodies are able to form a Mercury-like planet, fulfilling the necessary constraints in terms of mass and composition (silicate-to-iron mass ratio). We perform a series of smooth particle hydrodynamics (SPH) collision simulations. Our results show that it is possible to obtain Mercury-analogues from hit-and-run collisions involving a proto-Mercury roughly twice the mass of Mercury and targets of comparable mass (between 1 and 4 times higher), as long as the impact parameters (impact angle and velocity) are properly adjusted according to a set of well established scaling laws, while remaining compatible with the values typically observed in N-body simulations.