Type I Planetary Migration with MHD Turbulence

This paper examines how type I planetary migration is affected by the presence of turbulent density fluctuations in the circumstellar disk. For type I migration, the planet does not clear a gap in the disk and its secular motion is driven by torques generated by the wakes it creates in the surrounding disk fluid. MHD turbulence creates additional density perturbations that gravitationally interact with the planet and can dominate the torques that stem from the protoplanetary wake. This paper shows that conventional type I migration can be readily overwhelmed by turbulent perturbations, and hence the usual description of type I migration should be modified in locations where the magnetorotational instability is active. In general, the migrating planet does not follow a smooth inward trend but rather exhibits a random walk through phase space. Our main conclusion is that MHD turbulence will alter the timescales for type I planetary migration and, because of chaos, requires the timescales to be described by a distribution of values.