Planet formation
Abstract:
Planets form in so called protoplanetary discs that orbit newly born stars. These discs consist of gas and to a small fraction of micro-metre sized dust particles. These micro metre sized dust particles grow to pebbles (cm-dm in size) through collisions induced by velocity differences between the particles, where contact forces can lead to sticking. Very dense clouds of these pebbles can collapse under their own gravity and form planetesimals, which can be as big as Ceres. Planetary cores of a few Earth masses (like Jupiter's core) can form from accreting planetesimals or leftover pebbles. These planetary cores can then start to accrete a gaseous envelope and form gas giants like Jupiter and Saturn in our own solar system. Additionally, during their growth, planets also interact gravitationally with the surrounding gas disc, which leads to radial migration of planets inside the disc.
The process of giant planet formation has to happen during the lifetime of the protoplanetary disc, which is constraint to a few million years. During this time the disc is accreted onto the central star and loses mass and becomes colder, affecting the motion of particles and of the planetary cores inside the disc.
I will review theories of protoplanetary disc evolution and planet migration and formation.