From Hot Jupiters to Super-Earths via Roche Lobe Overflow

TL;DR

This paper explores how hot Jupiters can evolve into super-Earths through Roche lobe overflow, predicting observable intermediate planets and explaining the excess of small single-planet systems.

Contribution

It introduces detailed numerical models showing rapid planetary evolution via Roche lobe overflow, linking hot Jupiters to hot super-Earths and hot Neptunes.

Findings

Rapid envelope removal within a few Gyr

Existence of intermediate-mass planets at Roche limit

Potentially larger population of hot Jupiters than observed

Abstract

Through tidal dissipation in a slowly spinning host star the orbits of many hot Jupiters may decay down to the Roche limit. We expect that in most cases the ensuing mass transfer will be stable. Using detailed numerical calculations we find that this evolution is quite rapid, potentially leading to complete removal of the gaseous envelope in a few Gyr, and leaving behind an exposed rocky core ("hot super-Earth"). Final orbital periods are quite sensitive to the details of the planet's mass-radius relation, and to the effects of irradiation and photo-evaporation, but could be as short as a few hours, or as long as several days. Our scenario predicts the existence of planets with intermediate masses ("hot Neptunes") that should be found precisely at their Roche limit and in the process of losing mass through Roche lobe overflow. The observed excess of small single-planet candidate systems observed by Kepler may also be the result of this process. If so, the properties of their host stars should track those of the hot Jupiters. Moreover, the number of systems that produced hot Jupiters could be 2-3 times larger than one would infer from contemporary observations.