Tidal Heating of Extra-Solar Planets

TL;DR

This paper investigates the history and impact of tidal heating on close-in extra-solar planets, showing how it influences their physical properties and evolution, with implications for understanding their observed characteristics.

Contribution

It provides detailed models of tidal heating histories for several exoplanets, highlighting its significance in planetary evolution and physical properties, especially radius.

Findings

HD 209458 b may have experienced significant tidal heating affecting its radius.

GJ 876 d likely underwent tremendous heating, suggesting it may not be a solid planet.

Tidal heating is a large, time-varying factor in planetary evolution models.

Abstract

Extra-solar planets close to their host stars have likely undergone significant tidal evolution since the time of their formation. Tides probably dominated their orbital evolution once the dust and gas had cleared away, and as the orbits evolved there was substantial tidal heating within the planets. The tidal heating history of each planet may have contributed significantly to the thermal budget that governed the planet's physical properties, including its radius, which in many cases may be measured by observing transit events. Typically, tidal heating increases as a planet moves inward toward its star and then decreases as its orbit circularizes. Here we compute the plausible heating histories for several planets with measured radii, using the same tidal parameters for the star and planet that had been shown to reconcile the eccentricity distribution of close-in planets with other extra-solar planets. Several planets are discussed, including for example HD 209458 b, which may have undergone substantial tidal heating during the past billion years, perhaps enough to explain its large measured radius. Our models also show that GJ 876 d may have experienced tremendous heating and is probably not a solid, rocky planet. Theoretical models should include the role of tidal heating, which is large, but time-varying.