Migration of Protoplanets in Radiative Disks

Context. In isothermal disks the migration of protoplanets is directed inward. For small planetary masses the standard type I migration rates are so fast that this may result in an unrealistic loss of planets into the stars. Aims. We investigate the planet-disk interaction in non-isothermal disks and analyze the magnitude and direction of migration for an extended range of planet masses. Methods. We have performed detailed two-dimensional numerical simulations of embedded planets including heating/cooling effects as well as radiative diffusion for realistic opacities. Results. In radiative disks, small planets with Mplanet < 50MEarth do migrate outward with a rate comparable to absolute magnitude of standard type I migration. For larger masses the migration is inward and approaches the isothermal, type II migration rate. Conclusions. Our findings are particularly important for the first growth phase of planets and ease the problem of too rapid inward type-I migration.