Exoplanetology: Exoplanets & Exomoons

Halting the Migration of Super-Earths by Efficient Gap Opening in Radiative, Low Viscosity Disks

By Keith Cowing

Status Report

astro-ph.EP

March 3, 2025

Filed under astro-ph.EP, exoplanet, Protoplanetary Disk, super Earth

Halting the Migration of Super-Earths by Efficient Gap Opening in Radiative, Low Viscosity Disks — Left: conceptual “city map” of the different migration regimes for nearly inviscid disks α ≲ 10−5 as a function of the planet’s mass Mp and the dimensionless cooling timescale β. The left side mirrors the work of MN19a in isothermal disks, and the results discussed in this work straddle the transition between type-I and type-II regimes. The map only offers a qualitative overview without accounting for MHD, dust–gas interaction, or other processes, and the exact boundaries between different regimes are not necessarily sharp. Right: sketch of possible formation tracks for planets interior or exterior to the water snowline based on the regimes identified in the left panel. Depending on the planet’s initial location and its accretion efficiency, it is possible to form both rocky and icy super-Earths (‘SE’), mini-Neptunes (‘MN’), and gas giants. Their migration then stalls due to gap opening. The implications of radiative cooling in gap opening, while shown as a rather small blue box for Mp ≳ Mth in the left panel, actually determine every planet’s stalling location in the right panel. — astro-ph.EP

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.

Alexandros Ziampras, Richard P. Nelson, Sijme-Jan Paardekooper

Comments: 20 pages, 18 figures; submitted to MNRAS, suggestions and comments welcome
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2502.18564 [astro-ph.EP] (or arXiv:2502.18564v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2502.18564
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Submission history
From: Alexandros Ziampras
[v1] Tue, 25 Feb 2025 19:00:03 UTC (7,035 KB)
https://arxiv.org/abs/2502.18564
Astrobiology,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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