Migration of protoplanets in radiative discs

Context. In isothermal discs, the migration of protoplanets is directed inwards. For small planetary masses, the standard type I migration rates are so high that this can result in an unrealistic loss of planets into the stars. Aims. We investigate the planet-disc interaction in non-isothermal discs and analyse the magnitude and direction of migration for an extended range of planet masses. Methods. We performed detailed two-dimensional numerical simulations of embedded planets including heating/cooling effects as well as radiative diffusion for realistic opacities. Results. In radiative discs, small planets with $M_{\rm planet} < 50~M_{\rm Earth}$ migrate outwards at a rate comparable to the absolute magnitude of standard type I migration. For larger masses, the migration is inwards 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