The Frequency of Giant impacts on Earth-like Worlds

TL;DR

This study uses advanced N-body simulations to analyze the frequency and effects of giant impacts on Earth-like planets, revealing that such impacts are common and typically occur within the first 50 million years of planetary system development.

Contribution

The paper introduces a modified N-body simulation method that includes fragmentation and hit-and-run collisions, providing more realistic insights into planetary formation and impact histories.

Findings

Final planets have similar mass and number despite different collision histories.

Most Earth-analogs experience multiple impacts capable of atmospheric loss.

The median time for the last giant impact is about 43 million years, similar to Earth's Moon-forming event.

Abstract

The late stages of terrestrial planet formation are dominated by giant impacts that collectively influence the growth, composition and habitability of any planets that form. Hitherto, numerical models designed to explore these late stage collisions have been limited by assuming that all collisions lead to perfect accretion, and many of these studies lack the large number of realizations needed to account for the chaotic nature of N-body systems. We improve on these limitations by performing 280 simulations of planet formation around a Sun-like star, half of which used an N-body algorithm that has recently been modified to include fragmentation and hit-and-run (bouncing) collisions. We find that when fragmentation is included, the final planets formed are comparable in terms of mass and number, however their collision histories differ significantly and the accretion time approximately doubles. We explored impacts onto Earth-like planets which we parameterized in terms of their specific impact energies. Only 15 of our 164 Earth-analogs experienced an impact that was energetic enough to strip an entire atmosphere. To strip about half of an atmosphere requires energies comparable to recent models of the Moon-forming giant impact. Almost all Earth-analogs received at least one impact that met this criteria during the 2 Gyr simulations and the median was three giant impacts. The median time of the final giant impact was 43 Myr after the start of the simulations, leading us to conclude that the time-frame of the Moon-forming impact is typical amongst planetary systems around Sun-like stars.