Planet-Disk interaction in 3D: the importance of buoyancy waves

TL;DR

This study uses 3D hydrodynamic simulations to show that buoyancy waves significantly influence planet-disk interactions, especially in stratified disks with non-zero Brunt-Vaisala frequency, impacting planetary migration.

Contribution

It demonstrates the importance of buoyancy waves in 3D planet-disk interactions, revealing their substantial torque contribution in stratified protoplanetary disks.

Findings

Buoyancy waves are excited near planets in stratified disks with N≠0.

These waves can contribute up to 30-50% of the total planetary torque.

Buoyancy waves are likely common in dense inner regions of protoplanetary disks.

Abstract

We carry out local three dimensional (3D) hydrodynamic simulations of planet-disk interaction in stratified disks with varied thermodynamic properties. We find that whenever the Brunt-Vaisala frequency (N) in the disk is nonzero, the planet exerts a strong torque on the disk in the vicinity of the planet, with a reduction in the traditional "torque cutoff". In particular, this is true for adiabatic perturbations in disks with isothermal density structure, as should be typical for centrally irradiated protoplanetary disks. We identify this torque with buoyancy waves, which are excited (when N is non-zero) close to the planet, within one disk scale height from its orbit. These waves give rise to density perturbations with a characteristic 3D spatial pattern which is in close agreement with the linear dispersion relation for buoyancy waves. The torque due to these waves can amount to as much as several tens of per cent of the total planetary torque, which is not expected based on analytical calculations limited to axisymmetric or low-m modes. Buoyancy waves should be ubiquitous around planets in the inner, dense regions of protoplanetary disks, where they might possibly affect planet migration.