Turbulent Torques on Protoplanets in a Dead Zone
Dynamical migration of protoplanets seems likely to explain
the observed distribution of extrasolar planets. Previous work on
laminar disks predicts short migration times (less than the disk
lifetime). This is a significant problem for the "core accretion"
scenario, in which giant planets are thought to form from small,
rocky protoplanetary cores in the disk. However, there have been
recent suggestions that the turbulence providing accretion in
protoplanetary disks might enhance migration by turning laminar
migration into a random walk, possibly providing a solution to the
short migration timescale.
I will report the results of local, 3D simulations of MHD turbulence
with quiescent "dead zones" of varying sizes at the midplane. I
demonstrate that turbulent torques on a massless protoplanet at the
midplane are strongly affected by the presence of dead zones, which
considerably decrease the total turbulent torque on the planet. In
all cases, the torques have a finite correlation time and are
dominated by gas close to the planet. These results can be
incorporated into statistical models for the survival of a population
of protoplanets in a disk, allowing a better understanding of the
nature of planet migration and survival.