Forming Mercury by Giant Impacts

Abstract

Abstract The origin of Mercury’s high iron-to-rock ratio is still unknown. In this work we investigate Mercury’s formation via giant impacts and consider the possibilities of a single giant impact, a hit-and-run, and multiple collisions, in one theoretical framework. We study the standard collision parameters (impact velocity, mass ratio, impact parameter), along with the impactor’s composition and the cooling of the target. It is found that the impactor’s composition affects the iron distribution within the planet and the final mass of the target by up to 25%, although the resulting mean iron fraction is similar. We suggest that an efficient giant impact has to be head-on at high velocity, while in the hit-and-run case the impact can occur closer to the most probable collision angle (45°). It is also shown that Mercury’s current iron-to-rock ratio can be a result of multiple collisions, with their exact number depending on the collision parameters. Mass loss is found to be more significant when the collisions are close together in time.