Halting the migration of super-Earths by efficient gap opening in radiative, low viscosity disks

TL;DR

This study uses high-resolution radiation hydrodynamics simulations to show that radiative effects significantly influence the gap opening and migration behavior of super-Earths in nearly inviscid disks, affecting planetary system architectures.

Contribution

It provides the first detailed analysis of how radiative transfer impacts gap opening and migration regimes of super-Earths in low-viscosity disks, highlighting the importance of radiative effects in planet evolution.

Findings

Radiative cooling delays vortex formation at the gap edge.

Super-Earths can experience migration stalling due to radiative effects.

A migration regime map for radiative, nearly-inviscid disks is presented.

Abstract

While planet migration has been extensively studied for classical viscous disks, planet-disk interaction in nearly inviscid disks has mostly been explored with greatly simplified thermodynamics. In such environments, motivated by models of wind-driven accretion disks, even Earth-mass planets located interior to 1 au can significantly perturb the disk, carving gaps and exciting vortices on their edges. Both processes are influenced by radiative transfer, which can both drive baroclinic forcing and influence gap opening. We perform a set of high-resolution radiation hydrodynamics simulations of planet-disk interaction in the feedback and gap-opening regimes, aiming to understand the role of radiation transport in the migration of super-Earth-mass planets representative of the observed exoplanet population. We find that radiative cooling drives baroclinic forcing during multiple stages of the planet's migration in the feedback regime (~1.5 M_earth), significantly delaying the onset of vortex formation at the gap edge but ultimately resulting in type-III runaway migration episodes. For super-thermal-mass planets (~6.7 M_earth), radiative cooling is fundamentally linked to the gap opening process, with the planet stalling instead of undergoing vortex-assisted migration as expected from isothermal or adiabatic models. This stalling of migration can only be captured when treating radiative effects, and since it affects super-thermal-mass planets its implications for both the final configuration of planetary systems and population synthesis modeling are potentially huge. Combining our findings with previous related studies, we present a map of migration regimes for radiative, nearly-inviscid disks, with the cooling-mediated gap-opening regime playing a central role in determining the planet's orbital properties.