Disk-Planet Interaction Simulations: (I) Baroclinic Generation of Vortensity and Non-Axisymmetric Rossby-Wave-Instability

TL;DR

This study uses hydrodynamics simulations to explore how baroclinic instability generates vortensity and triggers Rossby-Wave-Instability in protoplanetary disks, affecting planet migration and disk structures.

Contribution

It demonstrates the widespread occurrence of vortensity generation via baroclinic instability and the robustness of Rossby-Wave-Instability across various disk conditions.

Findings

Vortensity is commonly generated in non-barotropic disks.

Rossby-Wave-Instability leads to non-axisymmetric density structures.

RWIs cause non-monotonic variations in planetary migration speed.

Abstract

We use a multi-dimensional 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 non-barotropic disks through the Baroclinic Instability, especially within the coorbital region. Our results also complement previous studies by \citet{KLL03} that non-axisymmetric RWIs are likely to develop at local minima of potential vorticity distribution that are generated by the interaction between a planet and a 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 non-axisymmetric density blobs, which exert stronger torques onto the planet when they travel in the vicinity of the planet. As a result of that, large amplitude oscillations are introduced to the time behavior of the total torque acted on the planet by the disk. In our current simulations, RWIs do not change the overall picture of inward orbital migration but bring in a non-monotonic 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.