Dynamics and Accretion of Planetesimals

TL;DR

This paper reviews the dynamics and growth processes of planetesimals, including simulations and models, to understand planetary system formation and the effects of disk gas on planet development.

Contribution

It provides a comprehensive overview of planetesimal dynamics, accretion modes, and the influence of disk gas, integrating N-body simulations with theoretical models.

Findings

Runaway growth leads to larger planetesimals forming faster.

Transition to oligarchic growth occurs after reaching a critical mass.

Dynamical effects of disk gas influence planet formation processes.

Abstract

We review the basic dynamics and accretion of planetesimals by showing N-body simulations. The orbits of planetesimals evolve through two-body gravitational relaxation: viscous stirring increases the random velocity and dynamical friction realizes the equiparation of the random energy. In the early stage of planetesimal accretion the growth mode of planetesimals is runaway growth where larger planetesimals grow faster than smaller ones. When a protoplanet (runaway-growing planetesimal) exceeds a critical mass the growth mode shifts to oligarchic growth where similar-sized protoplanets grow keeping a certain orbital separation. The final stage of terrestrial planet formation is collision among protoplanets known as giant impacts. We also summarize the dynamical effects of disk gas on planets and the core accretion model for formation of gas giants and discuss the diversity of planetary systems.