Orbital migration induced by anisotropic evaporation. Can hot Jupiters form hot Neptunes ?

TL;DR

This paper demonstrates that anisotropic atmospheric evaporation can cause significant orbital migration of close-in exoplanets, potentially explaining the observed differences in period distributions between hot Jupiters and hot Neptunes.

Contribution

The study provides an analytical framework showing how anisotropic evaporation can induce orbital migration, a mechanism previously overlooked in planetary evolution models.

Findings

Mass ejection can cause orbital period increase matching observed distributions.

Migration effect is significant if evaporation occurs above the hottest surface region.

Different period distributions of Jupiter- and Neptune-mass planets can be explained by evaporation-induced migration.

Abstract

Short period planets are subject to intense energetic irradiations from their stars. It has been shown that this can lead to significant atmospheric mass-loss and create smaller mass planets. Here, we analyse whether the evaporation mechanism can affect the orbit of planets. The orbital evolution of a planet undergoing evaporation is derived analytically in a very general way. Analytical results are then compared with the period distribution of two classes of inner exoplanets: Jupiter-mass planets and Neptune-mass planets. These two populations have a very distinct period distribution, with a probability lower than 10^-4 that they were derived from the same parent distribution. We show that mass ejection can generate significant migration with an increase of orbital period that matches very well the difference of distribution of the two populations. This would happen if the evaporation emanates from above the hottest region of planet surface. Thus, migration induced by evaporation is an important mechanism that cannot be neglected.