Orbital migration of protoplanets: The inertial limit

The dynamical evolution of a disk and the orbital migration of an embedded protoplanet are examined. We show how the migration of a protoplanet due to density waves torques can suppress the tendency for tidal truncation of the disk. A critical mass is determined as a function of the disk properties that represents the limiting mass that can sustain drift without stalling. This inertial limit is derived analytically, using a quasi-steady state theory, and confirmed by numerical experiment. This result contradicts the claim of Lin and Papaloizou that such a limit does not exist. Orbital mobility of objects due to density wave torques may have played an important role in the early evolution of the solar system.