Formation and Migration of Planets
Transit and radial velocity data indicate that a significant fraction (>10%) of solar-type stars may host planets with radii larger than 2 Rearth and with orbital periods shorter than 50 days. The assembly of a planet within ~0.25 AU of a solar-mass star is possible but requires a rather massive circum-stellar disk. However, the composition of super-Earths, which can be ice-dominated, and the occurrence of rocky and icy planets on closely adjacent orbits may argue against in situ formation. Hot Jupiters are also deemed to have originated elsewhere, because of their mass. It is then likely that some, if not most, of these planets formed at larger orbital distances and afterward moved closer to the star. One mechanism capable of explaining this long-range mobility is orbital migration driven by tidal torques exerted by a gaseous circum-stellar disk. I will discuss how observational results can be interpreted in light of current models of planet formation and migration in viscously evolving and photo-evaporating disks.