A "New Hope" for Moon Formation: Presenting a Multiple Impact Pathway

TL;DR

This paper proposes a multiple impact pathway for Moon formation, suggesting that several smaller impacts over time can produce a system similar to Earth and Moon, challenging the traditional single giant impact hypothesis.

Contribution

It introduces a novel multiple impact hypothesis and demonstrates through hydrodynamical simulations that several impacts can form a Moon-like system with higher compositional similarity.

Findings

Chains of impacts can produce Earth-Moon systems.

Multiple impacts achieve higher compositional similarity.

The scenario is a promising alternative to the giant impact hypothesis.

Abstract

The leading hypothesis for the origin of the Moon, that of a single giant impact, faces significant challenges. These include either the need for an impactor with a near-identical composition to Earth or an extremely high-mass or high-energy impact to achieve near-complete material mixing. In this paper we explore an alternative, the "multiple impact hypothesis", which relaxes the compositional constraints on both the target and projectile, and allows for the consideration of more probable, less extreme impacts that steadily grow the Earth and Moon to their current size over several impact events. Using the hydrodynamical code SWIFT, we simulate "chains" of impacts and follow the growth of a moon around a planet analogous to our own. Our results demonstrate that chains of three or more impacts can produce systems comparable to the Earth-Moon system whilst achieving higher compositional similarities than the canonical giant impact scenario. This presents the multiple impact hypothesis as a promising alternative to the single large impact scenario for the origin of the Moon.