Forming Mercury by Giant Impacts

TL;DR

This paper investigates Mercury's high iron-to-rock ratio through various giant impact scenarios, analyzing impact parameters, compositions, and collision sequences to understand its formation history.

Contribution

It introduces a comprehensive theoretical framework for Mercury's formation via giant impacts, considering multiple collision types and impact conditions.

Findings

Impactor composition influences iron distribution and mass loss.

Head-on impacts with high velocities are most effective for Mercury's formation.

Multiple collisions can explain Mercury's current iron-to-rock ratio.

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 15\%, although the resulting mean iron fraction is similar. We suggest that an efficient giant impact requires to be head-on with high velocities, while in the hit-and-run case the impact can occur closer to the most probable collision angle (45$^{\circ}$). 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 tight in time.