Streaming Torque in Dust-Gas Coupled Protoplanetary Disks

TL;DR

This paper studies how dust-gas interactions in protoplanetary disks influence planetary migration, revealing a dominant streaming torque that can cause outward movement of low-mass planets, potentially resolving rapid inward migration issues.

Contribution

It introduces a linear analysis of dust-gas coupled disks showing the dominance of streaming torque and its impact on planetary migration direction.

Findings

Streaming torque (ST) can induce outward planetary migration.

Dust-gas coupling strength influences total torque and migration.

Short radial wake caused by dust mode affects planet-disk interactions.

Abstract

We investigate the migration of low-mass protoplanets embedded in dust-gas coupled protoplanetary disks. Linear calculations are performed with respect to the NSH (Nakagawa-Sekiya-Hayashi 1986) equilibrium within a shearing sheet. We find that the dusty quasi-drift mode dominates the dynamical behaviors in close proximity to the protoplanet. This mode exhibits an extremely short radial wavelength, characterized by a dispersion relation of $ \tilde{\omega} = \left( 1 + \mu \right) \boldsymbol{W}_s \cdot \boldsymbol{k}$. The emergence of this mode leads to a wake with a short radial length-scale ahead of protoplanets, contributing to a positive torque, termed as ``Streaming Torque (ST)''. Furthermore, both Lindblad torque and corotation torque are affected by the NSH velocity. The total torque and planetary migration are contingent upon the coupling strength between dust and gas. In most scenarios, ST predominates, inducing outward migration for planets, thereby addressing the issue of rapid inward migration in their formation paradigm.