Dead Zones as Thermal Barriers to Rapid Planetary Migration in Protoplanetary Disks

TL;DR

This paper introduces a new thermal barrier mechanism caused by dead zones in protoplanetary disks that can significantly slow planetary migration, helping to explain the observed distribution of exoplanets.

Contribution

The study reveals that dead zones create a thermal barrier through back-heating effects, substantially reducing migration speeds in protoplanetary disks.

Findings

Dead zones produce a positive temperature gradient acting as a migration barrier.

The mechanism persists throughout the disk's lifetime.

Applicable to various planetary systems beyond the specific case analyzed.

Abstract

Planetary migration in standard models of gaseous protoplanetary disks is known to be very rapid ($\sim 10^5$ years) jeopardizing the existence of planetary systems. We present a new mechanism for significantly slowing rapid planetary migration, discovered by means of radiative transfer calculations of the thermal structure of protoplanetary disks irradiated by their central stars. Rapid dust settling in a disk's dead zone - a region with very little turbulence - leaves a dusty wall at its outer edge. We show that the back-heating of the dead zone by this irradiated wall produces a positive gradient of the disk temperature which acts as a thermal barrier to planetary migration which persists for the disk lifetime. Although we analyze in detail the migration of a Super-Earth in a low mass disk around an M star, our findings can apply to wide variety of young planetary systems. We compare our findings with other potentially important stopping mechanisms and show that there are large parameter spaces for which dead zones are likely to play the most important role for reproducing the observed mass-period relation in longer planetary periods.