A systematic survey of Moon-forming giant impacts: Non-rotating bodies

TL;DR

This systematic survey of Moon-forming impacts focuses on non-rotating bodies, identifying key impact parameters such as angular momentum and impact velocity that influence the formation of the Moon.

Contribution

It provides a comprehensive analysis of impact scenarios between non-rotating bodies, highlighting conditions necessary for Moon formation consistent with known constraints.

Findings

Impacts require a minimum angular momentum of about 2 J_EM.

Low-velocity impacts with high mass ratios are favored for isotopic similarity.

Non-rotating impact models can produce sufficient protolunar disks under specific conditions.

Abstract

In the leading theory of lunar formation, known as the giant impact hypothesis, a collision between two planet-size objects resulted in a young Earth surrounded by a circumplanetary debris disk from which the Moon later accreted. The range of giant impacts that could conceivably explain the Earth-Moon system is limited by the set of known physical and geochemical constraints. However, while several distinct Moon-forming impact scenarios have been proposed -- from small, high-velocity impactors to low-velocity mergers between equal-mass objects -- none of these scenarios have been successful at explaining the full set of known constraints, especially without invoking controversial post-impact processes. In order to bridge the gap between previous studies and provide a consistent survey of the Moon-forming impact parameter space, we present a systematic study of simulations of potential Moon-forming impacts. In the first paper of this series, we focus on pairwise impacts between non-rotating bodies. Notably, we show that such collisions require a minimum initial angular momentum budget of approximately $2~J_{EM}$ in order to generate a sufficiently massive protolunar disk. We also show that low-velocity impacts ($v_{\infty} \lesssim 0.5~v_{esc}$) with high impactor-to-target mass ratios ($\gamma \to 1$) are preferred to explain the Earth-Moon isotopic similarities. In a follow-up paper, we consider impacts between rotating bodies at various mutual orientations.