Probing the impact of varied migration and gas accretion rates for the formation of giant planets in the pebble accretion scenario

TL;DR

This study investigates how varying gas accretion rates and migration mechanisms influence giant planet formation, highlighting the importance of gas dynamics and disc viscosity in slowing migration and enabling planets to form farther from the star.

Contribution

It introduces the effects of gas accretion from the horseshoe region and dynamical torque into planet migration models, showing their significant impact on planetary growth and final orbital positions.

Findings

Lower disc viscosity leads to less inward migration.

Gas accretion from the horseshoe region promotes earlier gap opening.

Combining dynamical torque and horseshoe accretion significantly slows migration.

Abstract

The final orbital position of growing planets is determined by their migration speed, which is essentially set by the planetary mass. Small mass planets migrate in type I migration, while more massive planets migrate in type II migration, which is thought to depend mostly on the viscous evolution rate of the disc. A planet is most vulnerable to inward migration before it reaches type II migration and can lose a significant fraction of its semi-major axis at this stage. We investigated the influence of different disc viscosities, the dynamical torque and gas accretion from within the horseshoe region as mechanisms for slowing down planet migration. Our study confirms that planets growing in low viscosity environments migrate less, due to the earlier gap opening and slower type II migration rate. We find that taking the gas accretion from the horseshoe region into account allows an earlier gap opening and this results in less inward migration of growing planets. Furthermore, this effect increases the planetary mass compared to simulations that do not take the effect of gas accretion from the horseshoe region. Moreover, combining the effect of the dynamical torque with the effect of gas accretion from the horseshoe region, significantly slows down inward migration. Taking these effects into account could allow the formation of cold Jupiters (a > 1 au) closer to the water ice line region compared to previous simulations that did not take these effects into account. We thus conclude that gas accretion from within the horseshoe region and the dynamical torque play crucial roles in shaping planetary systems.