Influence of the disc structure on planet migration

Bertram Bitsch

In isothermal protoplanetary discs around young stars, low mass planets (a few M_E) migrate inwards to the star on a very short timescale (type-I-migration). Infact, the timescale is so short that these planets would be lost inside the star before they could form bigger objects due to gas accretion (e.g. Jupiter-size planets). In recent years, however, the relaxation of the isothermal approach and the inclusion of viscous heating and radiative cooling resulted in a change of the migration rate. In certain cases the migration rate can even be reversed so that low mass planets (above a few M_E) can migrate outwards, which allows them to stay longer in the gas disc and eventually form gas giant planets. This migration reversal is caused by the so-called corotation torque and is strongly dependent on the gradients of temperature and entropy in the disc. I will explain the mechanism of the corotation torque that causes outward migration and show the limits of this outward migration in discs. I will then show the difference between flared and self-shaddowed discs and what that implies for the migration of planets.