Dust Evolution and the Formation of Planetesimals

TL;DR

This paper reviews the early stages of planet formation, focusing on how tiny dust grains in protoplanetary disks grow into planetesimals, highlighting key physics, growth pathways, and recent observational progress.

Contribution

It synthesizes current understanding of dust growth physics and discusses potential pathways for planetesimal formation, integrating recent observational findings.

Findings

Dust grains grow from micrometers to planetesimals despite growth barriers.

Multiple pathways for planetesimal formation are considered.

Recent observations provide new insights into early planet formation stages.

Abstract

The solid content of circumstellar disks is inherited from the interstellar medium: dust particles of at most a micrometer in size. Protoplanetary disks are the environment where these dust grains need to grow at least 13 orders of magnitude in size. Our understanding of this growth process is far from complete, with different physics seemingly posing obstacles to this growth at various stages. Yet, the ubiquity of planets in our galaxy suggests that planet formation is a robust mechanism. This chapter focuses on the earliest stages of planet formation, the growth of small dust grains towards the gravitationally bound "planetesimals", the building blocks of planets. We will introduce some of the key physics involved in the growth processes and discuss how they are expected to shape the global behavior of the solid content of disks. We will consider possible pathways towards the formation of larger bodies and conclude by reviewing some of the recent observational advances in the field.