Torques Induced by Scattered Pebble-flow in Protoplanetary Disks

TL;DR

This paper demonstrates that dust dynamics in protoplanetary disks can exert significant torques on planetary cores, potentially halting or reversing inward migration and influencing planet formation, especially in higher-metallicity environments.

Contribution

It introduces the first torque map for dusty disks showing dust-induced effects on planetary migration, highlighting the importance of dust in planet formation models.

Findings

Dust-induced torques can halt inward migration.

Dust dynamics can induce outward planetary migration.

Dust torques scale with disk metallicity.

Abstract

Fast inward migration of planetary cores is a common problem in the current planet formation paradigm. Even though dust is ubiquitous in protoplanetary disks, its dynamical role in the migration history of planetary embryos has not been assessed. In this Letter, we show that the scattered pebble-flow induced by a low-mass planetary embryo leads to an asymmetric dust-density distribution that is able to exert a net torque. By analyzing a large suite of multifluid hydrodynamical simulations addressing the interaction between the disk and a low-mass planet on a fixed circular orbit, and neglecting dust feedback onto the gas, we identify two different regimes, gas- and gravity-dominated, where the scattered pebble-flow results in almost all cases in positive torques. We collect our measurements in a first torque map for dusty disks, which will enable the incorporation of the effect of dust dynamics on migration into population synthesis models. Depending on the dust drift speed, the dust-to-gas mass ratio/distribution and the embryo mass, the dust-induced torque has the potential to halt inward migration or even induce fast outward migration of planetary cores. We thus anticipate that dust-driven migration could play a dominant role during the formation history of planets. Because dust torques scale with disk metallicity, we propose that dust-driven outward migration may enhance the occurrence of distant giant planets in higher-metallicity systems.