Dynamical Evolution of the Earth-Moon Progenitors - Whence Theia?

TL;DR

This study uses numerical simulations to identify the initial orbital configurations of Theia that could have led to the Moon-forming impact, considering planetary resonances and early Solar System dynamics.

Contribution

It provides new insights into the initial orbital parameters of Theia and the dynamical pathways leading to the Moon-forming impact, incorporating planetary resonances and early planetary orbits.

Findings

Likely semimajor axis of Theia depends on Earth-Moon progenitor mass ratio.

Low eccentricities of terrestrial planets are linked to similar initial semimajor axes.

Mean motion resonances influence the timing and likelihood of the giant impact.

Abstract

We present integrations of a model Solar System with five terrestrial planets (beginning ~30-50 Myr after the formation of primitive Solar System bodies) in order to determine the preferred regions of parameter space leading to a giant impact that resulted in the formation of the Moon. Our results indicate which choices of semimajor axes and eccentricities for Theia (the proto-Moon) at this epoch can produce a late Giant Impact, assuming that Mercury, Venus, and Mars are near the current orbits. We find that the likely semimajor axis of Theia, at the epoch when our simulations begin, depends on the assumed mass ratio of Earth-Moon progenitors (8/1, 4/1, or 1/1). The low eccentricities of the terrestrial planets are most commonly produced when the progenitors have similar semimajor axes at the epoch when our integrations commence. Additionally, we show that mean motion resonances among the terrestrial planets and perturbations from the giant planets can affect the dynamical evolution of the system leading to a late Giant Impact.