Joint Astrophysics Colloquium

Joint Astrophysics Seminar

Origin of Giant Planets

Roman Rafikov

CITA

Recent numerous discoveries of extrasolar giant planets have brough into focus the question of their origin. At present there two competing theories of gian planet formation - core (nucleated) instability and gravitational instability. The former has much wider acceptance as it naturally explains the presence of dense cores in some giant planets and their enrichment in refractory materials. For a long time it has been thought though that planet formation via this avenue requires exceedingly long time. To address this issue a gravitational instability in a massive protoplanetary disk has been invoked as a means of forming planets directly. I will critically review these two ideas, emphasizing observational evidence of different kinds. I will also demonstrate that giant planets can hardly form by the gravitational instability at distances of less than tens of AU from their parent stars, leaving core instability as a much better candidate for the giant planet formation mechanism in the Solar System and the extrasolar systems discovered through the radial velocity searches.