Terrestrial planet formation from a ring

TL;DR

This study investigates the ring model for terrestrial planet formation through high-resolution simulations, finding that a concave gas disc profile helps maintain mass concentration at 1 AU, addressing radial dispersion issues.

Contribution

It demonstrates that a concave gas disc profile with a short lifetime can preserve mass concentration at 1 AU, improving the ring model for planet formation.

Findings

A ring of planetesimals tends to spread radially during accretion.

A concave gas disc profile with a peak at ~1 AU maintains mass concentration.

Short-lived gas discs (<1 Myr) prevent rapid Earth growth.

Abstract

It has been long proposed that, if all the terrestrial planets form within a tiny ring of solid material at around 1 AU, the concentrated mass-distance distribution of the current system can be reproduced. Recent planetesimal formation models also support this idea. In this study, we revisit the ring model by performing a number of high-resolution N-body simulations for 10 Myr of a ring of self-interacting planetesimals, with various radial distributions of the gas disc. We found that even if all the planetesimals form at ~1 AU in a minimum mass solar nebula-like disc, the system tends to spread radially as accretion proceeds, resulting in a system of planetary embryos lacking mass-concentration at ~1 AU. Modifying the surface density of the gas disc into a concave shape with a peak at ~1 AU helps to maintain mass concentrated at ~1 AU and solve the radial dispersion problem. We further propose that such a disc should be short lived (<= 1 Myr) and with a shallower radial gradient in the innermost region (< 1 AU) than previously proposed to prevent a too-rapid growth of Earth. Future studies should extend to ~100 Myr the most promising simulations and address in a self-consistent manner the evolution of the asteroid belt and its role in the formation of the terrestrial planets.