Institute for Advanced Study Informal Astrophysics Seminar - DIFFERENT DAY

The discovery of more than 400 extrasolar planets keeps challenging the theory of planet formation. Multi-planetary systems are of particular interest. Their orbital parameters allow us to constrain properties of the otherwise unobservable formation phase. I will show that the planetary system HD45364 had to be formed in a massive protoplanetary disc in order to avoid the 2:1 resonance and get captured in the observed 3:2 resonance. The system HD128311, however, had to be formed in a very turbulent disc. The turbulence (very likely due to the MRI) was strong enough to almost completely destroy the resonance. Using such coherent formation scenarios, one can also reduce the dimensionality of the parameter space dramatically when fitting orbits to observed radial velocity curves. This procedure gives a better fit to the observed RV data and furthermore provides the first testable predictions of orbital parameters from planet formation theory. Saturn's rings are a small scale version of a protoplanetary disc. We can observe the same phenomena as in protoplanetary disc but in real time, because one orbit is extremely short (13 hours). The Cassini spacecraft discovered several small moonlets in the A-ring. Similar to proto-planets, they are subject to orbital migration. Depending on the properties of the ring particles, this migration can be laminar or stochastic. Monitoring the random walk provides interesting clues on the nature of the ring particles. I present new results using analytic and numerical models that will help to determine the origin of Saturn's rings: moonlets consist of fragments from a catastrophic event in Saturn's past.