How to Build the Building Blocks of Planets

Christian Lenz, Max-Planck-Institute for Astronomy, Heidelberg, Germany

Planet formation is a strongly growing field in the community of astrophysics and astronomy with a lot of open questions… and it is a dirty business. First of all, planets are made out of the dirt we call interstellar dust, embedded in gaseous disks around young stars. Secondly, the physics involved is not ‘‘clean’’ in a sense that neither all the forces and effects involved, nor all the initial conditions of this process are known. In the early stage of planet formation, micron sized dust grains grow to so-called pebbles with typical sizes of mm-dm. But once the grains have reached a critical size, they stop growing around dm size due to growth barriers. It is believed that planets are formed by so-called “planetesimals”, objects being bound by their own gravitational attraction rather than surface and material binding forces, and being the smallest building bricks of planets. Since we need to reach several km in size of the planetesimals, there is a missing link in the growth process from pebbles to planet(esimal)s. I will discuss the basics for grain growth and present a novel model for planetesimal formation we developed in Heidelberg. Our obtained radial planetesimal distribution allows to test the otherwise free disk parameters (disk size, disk mass, level of turbulence, …) of the Solar Nebula by comparing the predicted initial planetesimal distribution with constraints from the Solar System.