Halting Migration in Magnetospherically Sculpted Protoplanetary Disks

TL;DR

This paper models how stellar magnetic fields influence the inner edge of protoplanetary disks, creating migration traps that explain the observed distribution of close-in super-Earths and sub-Neptunes.

Contribution

It introduces a physically motivated model of magnetic field diffusion shaping the disk edge and demonstrates its impact on planetary migration and final positions.

Findings

Magnetic field strengths of 67-180G match observed planet distribution features.

Migration traps are formed at the outer edge of the transition zone.

Final planet locations correlate with the stellar magnetic budget.

Abstract

We present a physically motivated model for the manner in which a stellar magnetic field sculpts the inner edge of a protoplanetary disk, and examine the consequence for the migration and stopping of sub-Neptune and super-Earth planets. This model incorporates a transition zone exterior to the inner truncation of the disk, where the surface density profile is modified by the diffusion of the stellar magnetic field into the disk. This modification results in a migration trap at the outer edge of the transition zone. We performed simulations of single planet migration, considering a range of stellar magnetic field strengths and magnetic diffusion profiles. Our simulations show a tight relationship between the final locations of planets and the total magnetic budget available for the disk from their host star. We found that a stellar magnetic field between 67 to 180G and a power-law index between 3 and 2.75 can reasonably reproduce the location at which the observed occurrence rate of close-in Super-Earth and Sub-Neptune populations changes slope.