The Formation of Planets

Abstract

Mankind has attempted to understand the origin of the Earth and planets for countless generations. In the past few decades, starting largely from the pioneering work of Safronov in the 1960s, philosophical speculation about their birth has been replaced with detailed analytical and numerical simulations whose goal is to reproduce the observed properties of our own solar system. With the recent groundbreaking discoveries of planets around ordinary stars like our Sun (Mayor & Queloz 1995; Marcy & Butler 1996; Butler & Marcy 1996; see also the review by Marcy in this volume), we now have a reasonable sample of nearby planetary systems that we can use to test and validate theoretical models and from which we can learn new and unexpected features of planet formation. In the upcoming decade the launches of NASA’s Space Interferometry Mission (SIM) and ESA’s Global Astrometric Interferometer for Astrophysics (GAIA) (and their longer term counterparts Terrestrial Planet Finder [TPF] and Infrared Space Interferometry Mission [IRSI]) will allow us to detect directly planets around nearby stars, which will give us an even more complete census of the number and content of planetary systems in the Solar neighborhood. To place this observational data in a proper astrophysical context, we need to understand how planets are born and how they interact with their environment. In this review, I will discuss the dynamics of the growth of solid particles from initially micron-sized dust grains through kilometer-sized planetesimals to their final planetary mass. I will also discuss the formation of the gas-rich giant planets and their tidal interaction with the surrounding nebular disk. The reader interested in further details of the planet formation process is encouraged to consult the excellent reviews by Lissauer (1993) and by Marcy and Butler (1998).