Tidal migration of exoplanets around M-dwarfs: frequency-dependent tidal dissipation

TL;DR

This study models tidal dissipation in M-dwarfs to understand how it influences the orbital migration of close-in exoplanets, revealing resonance effects that shape planetary system architectures.

Contribution

It introduces a non-perturbative spectral method to accurately compute frequency-dependent tidal dissipation in fully-convective M-dwarfs, incorporating mode coupling effects.

Findings

Resonance locking significantly influences orbital migration.

Predicted dearth of planets within certain orbital periods.

Orbital decay and outward migration depend on planet mass and period.

Abstract

The orbital architectures of short-period exoplanet systems are shaped by tidal dissipation in their host stars. For low-mass M-dwarfs whose dynamical tidal response comprises a dense spectrum of inertial modes at low frequencies, resolving the frequency dependence of tidal dissipation is crucial to capturing the effect of tides on planetary orbits throughout the evolutionary stages of the host star. We use non-perturbative spectral methods to calculate the normal mode oscillations of a fully-convective M-dwarf modeled using realistic stellar profiles from MESA. We compute the dissipative tidal response composed of contributions from each mode as well as non-adiabatic coupling between the modes, which we find to be an essential component of the dissipative calculations. Using our results for dissipation, we then compute of the evolution of circular, coplanar planetary orbits under the influence of tides in the host star. We find that orbital migration driven by resonance locking affects the orbits of Earth-mass planets at orbital periods $P_{\rm orb} \lesssim 1.5$ day and of Jupiter-mass planets at $P_{\rm orb} \lesssim 2.5$ day. Due to resonantly-driven orbital decay and outward migration, we predict a dearth of small planets closer than $P_{\rm orb} \sim 1$ day and similarly sparse numbers of more massive planets out to $P_{\rm orb} \sim 3$ day.