2007ApJ...667.1220O

We use a multidimensional hydrodynamics code to study the gravitational interaction between an embedded planet and a protoplanetary disk, with emphasis on the generation of vortensity (potential vorticity) through a baroclinic instability and subsequent development of Rossby wave instability (RWI). It is found that the generation of potential vorticity is very common and effective in nonbarotropic disks through the baroclinic instability, especially within the co-orbital region. Our results also complement previous studies by Koller and coworkers, which showed that nonaxisymmetric RWIs are likely to develop at local minima of potential vorticity distribution that are generated by the interaction between a planet and an inviscid barotropic disk. This second instability appears to be very common and robust, regardless of the equation of state, initial density distribution, and rotational law of the disk. The development of RWIs results in nonaxisymmetric density blobs, which exert stronger torques on the planet when they travel within its vicinity. As a result of that, large-amplitude oscillations are introduced to the time behavior of the total torque acting on the planet from the disk. In our current simulations, RWIs do not change the overall picture of inward orbital migration, but bring in a nonmonotonic behavior to the migration speed. As a side effect, RWIs also introduce interesting structures into the disk. These structures may help the formation of Earth-like planets in the habitable zone, or hot Earths interior to a close-in giant planet.