Predicting the observational signature of migrating Neptune-sized planets in low-viscosity disks

TL;DR

This study demonstrates that the migration behavior of Neptune-sized planets in low-viscosity disks can be inferred from dust ring structures imprinted in the disk, which are observable with current ALMA capabilities.

Contribution

It introduces a method to diagnose planet migration by analyzing dust density structures in protoplanetary disks through hydrodynamical and radiative transfer simulations.

Findings

Neptune-sized planets can create multiple dust rings in low-viscosity disks.

The spacing of dust rings correlates with the planet's migration speed and direction.

Different migration scenarios are distinguishable with ALMA observations.

Abstract

The migration of planetary cores embedded in a protoplanetary disk is an important mechanism within planet-formation theory, relevant for the architecture of planetary systems. Consequently, planet migration is actively discussed, yet often results of independent theoretical or numerical studies are unconstrained due to the lack of observational diagnostics designed in light of planet migration. In this work we follow the idea of inferring the migration behavior of embedded planets by means of the characteristic radial structures that they imprint in the disk's dust density distribution. We run hydrodynamical multifluid simulations of gas and several dust species in a locally isothermal $\alpha$-disk in the low-viscosity regime ($\alpha=10^{-5}$) and investigate the obtained dust structures. In this framework, a planet of roughly Neptune mass can create three (or more) rings in which dust accumulates. We find that the relative spacing of these rings depends on the planet's migration speed and direction. By performing subsequent radiative transfer calculations and image synthesis we show that - always under the condition of a near-inviscid disk - different migration scenarios are, in principle, distinguishable by long-baseline, state-of-the-art ALMA observations.