Michiel Lambrechts - September 23, 2016

Formation of the giant planets in the Solar System

In the core accretion scenario for giant planets, cores need to grow rapidly and attract
gaseous envelopes before the gas disc around the young star dissipates. We have found
that, after the formation of large planetesimals, embryos can rapidly grow by sweeping
up small cm-sized particles. While pebbles pass the core, the damping effect of gas drag
greatly increases the accretion cross section compared to planetesimals. This allows
cores to form, at orbits wider than Jupiter, within a few million year. We will also
discuss how this process of pebble accretion leaves an imprint on the small body
population in the asteroid belt and Kuiper belt.
Finally, as planetary cores reach completion, they start attracting a gaseous
atmosphere. Ice giants (and their close-in exoplanet analogues) keep their low-mass
envelopes, while gas giants do not. This difference can be explained by the cores of the
gas giants getting isolated from pebbles early on. Without the additional energy release
by solid accretion, the envelope can contract and trigger runaway gas accretion.