Giant planet migration in viscous power-law disks

Many extrasolar planets discovered over the past decade are gas giants in tight orbits around their host stars. Due to the difficulties of forming these "hot Jupiters'' in situ, they are generally assumed to have migrated to their present orbits through interactions with their nascent disks. In this paper, we present a systematic study of giant planet migration in power-law disks. We find that the planetary migration rate is proportional to the disk surface density. This is inconsistent with the assumption that the migration rate is simply the viscous drift speed of the disk. However, this result can be obtained by balancing the angular momentum of the planet with the viscous torque in the disk. We have verified that this result is not affected by adjusting the resolution of the grid, the smoothing length used, or the time at which the planet is released to migrate.