Protoplanetary migration in turbulent isothermal disks

TL;DR

This study investigates how turbulence in protoplanetary disks affects the migration of low-mass planets, showing that turbulence can sustain the horseshoe drag and influence planetary migration behavior.

Contribution

It introduces a turbulence model in hydrodynamic simulations demonstrating how turbulence sustains horseshoe drag, affecting planetary migration in protoplanetary disks.

Findings

Turbulence can keep the horseshoe drag unsaturated over long periods.

Vortensity diffusion models the desaturation of the horseshoe drag.

Differences in torque arise at high turbulence due to density profile evolution.

Abstract

In order to reproduce the statistical properties of the observed exoplanets, population synthesis models have shown that the migration of protoplanets should be significantly slowed down, and that processes stalling migration should be at work. Much current theoretical efforts have thus been dedicated to find physical effects that slow down, halt or even reverse migration. Many of these studies rely on the horseshoe drag, whose long term-evolution (saturated or not) is intimately related to the disk viscosity in laminar disk models. We investigate how the horseshoe drag exerted on a low-mass planet is altered by a more realistic treatment of the turbulence in protoplanetary disks. Two-dimensional hydrodynamic simulations are performed with a turbulence model that reproduces the main turbulence properties of three-dimensional magnetohydrodynamic calculations. We find that the horseshoe drag can remain unsaturated on the long term, depending on the turbulence strength. We show that the desaturation of the horseshoe drag by turbulence can be modeled by vortensity diffusion across the time-averaged planet's horseshoe region. At low-turbulence, the running-time averaged torque is in good agreement with the total torque obtained for an equivalent laminar model, with a similar vortensity's diffusion coefficient. At high-turbulence, differences arise due to the time-evolution of the averaged density profile with turbulence.