On the growth and orbital evolution of giant planets in layered protoplanetary disks

TL;DR

This study uses 3D hydrodynamic simulations to investigate how dead-zones in protoplanetary disks influence the growth and migration of giant planets, revealing that dead-zone size affects migration rates but not growth timescales.

Contribution

It provides new insights into the impact of dead-zone vertical extent on planetary accretion and migration, highlighting the weak dependence of growth timescales on dead-zone size.

Findings

Growth timescale is independent of dead-zone size.

Migration slows with larger dead-zones for Jupiter-mass planets.

Migration of Saturn-mass planets is weakly affected by dead-zone size.

Abstract

We present the results of hydrodynamic simulations of the growth and orbital evolution of giant planets embedded in a protoplanetary disk with a dead-zone. The aim is to examine to what extent the presence of a dead-zone affects the rates of mass accretion and migration for giant planets. We performed 3D numerical simulations using a grid-based hydrodynamics code. In these simulations of non-magnetised disks, the dead-zone is treated as a region where the vertical profile of the viscosity depends on the distance from the equatorial plane. We consider dead-zones with vertical sizes, H_dz, ranging from 0 to H_dz=2.3H, where H is the disk scale-height. For all models, the vertically integrated viscous stress, and the related mass flux through the disk, have the same value, such that the simulations test the dependence of planetary mass accretion and migration on the vertical distribution of the viscous stress. For each model, an embedded 30 earth-masses planet on a fixed circular orbit is allowed to accrete gas from the disk. Once the planet mass becomes equal to that of Saturn or Jupiter, we allow the planet orbit to evolve due to gravitational interaction with the disk. We find that the time scale over which a protoplanet grows to become a giant planet is essentially independent of the dead-zone size, and depends only on the total rate at which the disk viscously supplies material to the planet. For Saturn-mass planets, the migration rate depends only weakly on the size of the dead-zone for H_dz< 1.5H, but becomes slower when H_dz=2.3H. This effect is due to the desaturation of corotation torques which originate from residual material in the partial-gap region. For Jupiter-mass planets, there is a clear tendency for the migration to proceed more slowly as the size of the dead-zone increases.