# Tidal heating and stellar irradiation of Hot Jupiters

## TL;DR

This paper investigates how stellar irradiation and tidal heating interact in Hot Jupiters, revealing a thermomechanical feedback mechanism that can explain their observed radius inflation over billions of years.

## Contribution

It introduces an analytical model demonstrating the coupling of vibrational modes with thermal evolution, explaining planetary bloating through resonant tidal heating and stellar irradiation effects.

## Key findings

- Tidal models produce interior radiative zones and enhanced mode dissipation.
- Stellar irradiation traps heat at depth, increasing planetary entropy and radius.
- Thermally driven winds help maintain spherical atmospheric structure.

## Abstract

We study the interaction between stellar irradiation and tidal heating in gaseous planets with short orbital periods. The intentionally simplified atmospheric model we employ makes the problem analytically tractable and permits the derivation of useful scaling relations. We show that many tidal models provide thermal feedback, producing interior radiative zones and leading to enhanced g-mode dissipation with a wide spectrum of resonances. These resonances are dynamically tuned by the thermal feedback, and so represent a novel form of thermomechanical feedback, coupling vibrational modes to the very slow thermal evolution of the planet. We then show that stellar irradiation allows the heat produced by these modes to be trapped at depth with high efficiency, leading to entropy increase in the central convective region, as well as expansion of the planet's radius sufficient to match observed swelling. We find that thermally driven winds play an essential role in this process by making the thermal structure of the atmosphere spherically symmetric within a few scale heights of the photosphere. We characterise the relationship between the swelling factor, the orbital period and the host star and determine the timescale for swelling. We show that these g-modes suffice to produce bloating on the order of the radius of the planet over $\mathrm{Gyr}$ timescales when combined with significant insolation and we provide analytic relations for the relative magnitudes of tidal heating and insolation.