Planetary Formation and Evolution

Over the course of the last two decades, few astronomical discoveries have generated broader interest than the detection and characterization planetary systems that encircle other stars. The basic properties of the majority of these planets are different from those of our own solar system in a number of ways: extrasolar worlds have orbital periods that are measured in days rather than years; have masses that exceed the Earth by a factor of a few; appear to be silicate-rich though routinely possessing substantial Hydrogen-Helium atmospheres; and frequently occur in multiples. Beyond these basic attributes, recent work has revealed that short-period extrasolar planets exhibit an intriguing pattern of intra-system uniformity, which stands in sharp contrast with the staggering overall diversity of the Galactic Planetary Census. In this talk, I will discuss a new theoretical picture for planet formation that satisfies the aforementioned constraints. Building upon recent work — which demonstrates that planetesimals can form rapidly at discrete locations in the disk — we propose that super-Earths originate inside rings of silicate-rich planetesimals at approximately ~1 AU. Within the context of this picture, we show that planets grow primarily through pairwise collisions, until they achieve terminal masses that are regulated by isolation and orbital migration. Numerical simulations carried out within this theoretical framework produce synthetic planetary systems that bear a close resemblance to the observed population of short-period extrasolar planets. I will further discuss how this model fits into the broader context of the formation of the terrestrial planets of the solar system as well as the Galilean satellites.