  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. 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. We
have performed detailed two-dimensional numerical simulations of embedded
planets including heating/cooling effects as well as radiative diffusion for
realistic opacities.
  In radiative disks, small planets with M_planet < 50 M_Earth 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. Our findings are particularly important for
the first growth phase of planets and ease the problem of too rapid inward
type-I migration.
