Outward migration of a super-Earth in a disc with outward propagating density waves excited by a giant planet

TL;DR

This paper introduces a new mechanism where outward-propagating density waves excited by a giant planet can halt or reverse the inward migration of a super-Earth, affecting planetary system formation.

Contribution

It demonstrates how density waves from a giant planet can stop or reverse super-Earth migration, supported by hydrodynamical and shearing box simulations.

Findings

Outward density waves can halt inward migration of super-Earths.

Migration reversal is possible under certain disc conditions.

Implications for formation of systems like GJ876.

Abstract

In this paper we consider a new mechanism for stopping the inward migration of a low-mass planet embedded in a gaseous protoplanetary disc. It operates when a low-mass planet (for example a super-Earth), encounters outgoing density waves excited by another source in the disc. This source could be a gas giant in an orbit interior to that of the low-mass planet. As the super-Earth passes through the wave field, angular momentum is transferred to the disc material and then communicated to the planet through coorbital dynamics, with the consequence that its inward migration can be halted or even reversed. We illustrate how the mechanism we consider works in a variety of different physical conditions employing global two-dimensional hydrodynamical calculations. We confirm our results by performing local shearing box simulations in which the super-Earth interacts with density waves excited by an independent harmonically varying potential. Finally, we discuss the constraints arising from the process considered here, on formation scenarios for systems containing a giant planet and lower mass planet in an outer orbit with a 2:1 commensurability such as GJ876.