Dynamical corotation torques on low-mass planets

TL;DR

This paper investigates how dynamical corotation torques influence the migration of low-mass planets in protoplanetary discs, revealing they can significantly alter migration paths, especially in more massive discs, potentially enlarging outward migration zones.

Contribution

It introduces the concept of dynamical corotation torques and demonstrates their significant impact on planet migration in more massive discs, extending previous static torque analyses.

Findings

Dynamical torques can slow down inward migration.

Dynamical torques can cause runaway outward migration.

Outward migration regions are larger when dynamical effects are considered.

Abstract

We study torques on migrating low-mass planets in locally isothermal discs. Previous work on low-mass planets generally kept the planet on a fixed orbit, after which the torque on the planet was measured. In addition to these static torques, when the planet is allowed to migrate it experiences dynamical torques, which are proportional to the migration rate and whose sign depends on the background vortensity gradient. We show that in discs a few times more massive than the Minimum Mass Solar Nebula, these dynamical torques can have a profound impact on planet migration. Inward migration can be slowed down significantly, and if static torques lead to outward migration, dynamical torques can take over, taking the planet beyond zero-torque lines set by saturation of the corotation torque in a runaway fashion. This means the region in non-isothermal discs where outward migration is possible can be larger than what would be concluded from static torques alone.