# Planetesimals to Terrestrial Planets: collisional evolution amidst a dissipating gas disk

## TL;DR

This study uses numerical simulations to explore how collisional evolution and a dissipating gas disk influence the inside-out growth of terrestrial planets, revealing complex growth patterns and mass distribution effects.

## Contribution

It demonstrates that the entire inner disk does not reach a simple bi-modal distribution and highlights the impact of collisional grinding and gas dissipation on planet formation.

## Key findings

- Inner disk growth is inside-out and varies spatially.
- Collisional grinding significantly alters surface density and mass ratios.
- Embryos remain stable for 10-20 Myr before chaotic growth begins.

## Abstract

We present numerical simulations of terrestrial planet formation that examine the growth continuously from planetesimals to planets in the inner Solar System. Previous studies show that the growth will be inside-out, but it is still common practice to assume that the entire inner disk will eventually reach a bi-modal distribution of embryos and planetesimals. For the combinations of disk mass, initial planetesimal radius and gas disk lifetime explored in this work the entire disk never reaches a simple bi-modal mass distribution. We find that the inside-out growth is amplified by the combined effects of collisional evolution of solid bodies and interactions with a dissipating gas disk. This leads to oligarchic growth never being achieved in different places of the disk at the same time, where in some cases the disk can simultaneoulsy support chaotic growth and giant impacts inside 1 au and runaway growth beyond 2 au. The planetesimal population is efficiently depleted in the inner disk where embryo growth primarily advances in the presence of a significant gas disk. Further out in the disk growth is slower relative to the gas disk dissipation, resulting in more excited planetesimals at the same stage of growth and less efficient accretion. This same effect drives mass loss due to collisional grinding strongly altering the surface density of the accreted planets relative to the initial mass distribution. This effect decreases the Mars-to-Earth mass ratios compared to previous works with no collisional grinding. Similar to some previous findings utilizing vastly different growth scenarios these simulations produce a first generation of planetary embryos that are stable for 10-20 Myr, or 5-10 e-folding times of the gas dissipation timescale, before having an instability and entering the chaotic growth stage.