From Dust to Planetesimals

Abstract

It is now clear that on average every star in the Milky Way has at least one planet. Planet formation seems to be an inevitable side effect of the star formation process. However, there are several problems that make it difficult to understand how the primordial micrometer dust grains observed in protoplanetary disks are turned to planets. One of them is the formation of kilometer-sized planetesimals, which is the topic of this dissertation. We first develop a new code for dust evolution in protoplanetary disks, which is based on the Monte Carlo approach. The code is then used to model several possible planetesimal formation scenarios. We test planetesimal formation by both dust coagulation and gravitational collapse of dense pebble clumps formed by the streaming instability. We examine what conditions are necessary for these scenarios to proceed and compare their planetesimal formation efficiencies. Our results suggest that planetesimal formation via dust coagulation is possible in the inner part of the protoplanetary disk, whereas the streaming instability may only be efficient beyond the snow line. Our predictions can be used to model the late stages of planet formation.