3D MHD simulations of planet migration in cavities and inner discs of magnetized stars

TL;DR

This study uses 3D MHD simulations to explore how magnetic fields of young stars influence planet migration, revealing mechanisms that can slow, halt, or reverse inward planetary movement near star magnetospheres.

Contribution

It provides the first detailed 3D MHD simulation analysis of planet migration in magnetized star environments, highlighting effects of magnetic fields on migration behavior.

Findings

Planets in cavities migrate inward until resonances are inside the cavity.

Migration can stall or reverse near the disc-cavity boundary.

Magnetosphere interactions can slow or reverse planet migration.

Abstract

We investigate the Type I migration of planets in low-density cavities and inner discs of strongly magnetized young stars using global three-dimensional (3D) magnetohydrodynamic (MHD) simulations, where the strong magnetic field carves the low-density cavity. Simulations show that a planet in the cavity migrates inwards up to the radius at which the outer Lindblad resonances are inside the cavity. At smaller radii, the migration stalls. The migration is faster if a star accretes in the unstable regime where the temporary tongues penetrate the magnetosphere. If a planet is in a highly inclined orbit, it interacts with the disc, and the eccentricity increases due to the Kozai-Lydov mechanism. A planet may stop or reverse its migration in the inner disc before entering the cavity. The magnetosphere interacts with the inner disc, changing its density distribution such that migration slows down or is even reversed. A tilted magnetosphere also excites density and bending waves in the disc, which may slow down migration and also increase the inclination and eccentricity of the planet. When a planet reaches the disc-cavity boundary, it is typically trapped at the boundary by asymmetric corotation torque. A planet moves together with the boundary when the cavity expands. Overall, a magnetized star provides an environment for slow or reverse migration.