Planet Migration and Disk Destruction due to Magneto-Centrifugal Stellar Winds

TL;DR

This paper explores how magneto-centrifugal stellar winds from young stars influence the inward or outward migration of close-in giant planets and contribute to disk erosion, with implications for planetary system evolution.

Contribution

It introduces a model linking stellar wind properties to planetary migration directions and timescales, highlighting the role of magnetic wind configurations and stellar rotation.

Findings

Planets beyond 0.06 AU tend to migrate outward.

Migration timescale estimated as 2-20 million years.

Disk erosion occurs over 1-100 million years.

Abstract

This paper investigates the influence of magneto-centrifugally driven or simply magnetic winds of rapidly-rotating, strongly-magnetized T Tauri stars in causing the inward or outward migration of close-in giant planets. The azimuthal ram pressure of the magnetized wind acting on the planet tends to increase the planet's angular momentum and cause outward migration if the star's rotation period $P_*$ is less than the planet's orbital period $P_p$. In the opposite case, $P_* > P_p$, the planet migrates inward. Thus, planets orbiting at distances larger (smaller) than $0.06 {\rm AU}(P_*/5{\rm d})^{2/3}$ tend to be pushed outward (inward), where $P_*$ is the rotation period of the star assumed to have the mass of the sun. The magnetic winds are likely to occur in T Tauri stars where the thermal speed of the gas close to the star is small, where the star's magnetic field is strong, and where the star rotates rapidly. The time-scale for appreciable radial motion of the planet is estimated as $\sim 2 - 20$ Myr. A sufficiently massive close-in planet may cause tidal locking and once this happens the radial migration due to the magnetic wind ceases. The magnetic winds are expected to be important for planet migration for the case of a multipolar magnetic field rather than a dipole field where the wind is directed away from the equatorial plane and where a magnetospheric cavity forms. The influence of the magnetic wind in eroding and eventually destroying the accretion disk is analyzed. A momentum integral is derived for the turbulent wind/disk boundary layer and this is used to estimate the disk erosion time-scale as $\sim 1-10^2$ Myr, with the lower value favored.