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

Abstract We investigate 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 outer parts of the cavity migrates faster due to remote interaction with the disc at the outer Lindblad resonances. In the inner parts of the cavity, the migration stalls. If a star accretes in the unstable regime, then migration is slightly faster due to planet’s interaction with unstable tongues. The star’s magnetosphere changes the density distribution in the inner disc, and migration is slower than in the outer disc. The migration stops at the disc-cavity boundary due to one-sided corotation torque. Overall, a low-density cavity, the disc-cavity boundary, and the inner disc provide conditions for slow migration and may help planets to survive until the disc disperses. This may explain the existence and survival of many close-in planets. If a planet is in a highly inclined orbit, it interacts with the disc, and the eccentricity increases due to the Kozai-Lidov mechanism. A tilted magnetosphere also excites density and bending waves in the disc, which slightly increase the inclination and eccentricity of the planet.