Migration of protoplanets: Effects on terrestrial planet formation

I review the role of planetary migration on the formation process of terrestrial planets. I first show a simple estimation for growth timescale of solid proto-planets and review a linear theory of disk–planet gravitational interaction to estimate the migration rate of proto-planets in a gas disk, and then discuss the difficulty of the formation of terrestrial planets in terms of comparison between migration timescale and growth timescale. Next I show recent studies which suggest possible mechanisms to solve the problem. I briefly discuss the formation process of Mercury in the context of terrestrial-planet formation.