Increased Heat Transport in Ultra-Hot Jupiter Atmospheres Through H$_2$ Dissociation/Recombination

TL;DR

This paper investigates how hydrogen dissociation and recombination in ultra-hot Jupiter atmospheres enhance heat transport from day to night, affecting atmospheric dynamics and energy distribution.

Contribution

It introduces a simple energy balance model showing that H$_2$ dissociation/recombination significantly increases heat recirculation in UHJs, a novel insight into their atmospheric processes.

Findings

H$_2$ dissociation/recombination boosts heat transport efficiency.

Recombination acts like latent heat, aiding energy transfer.

Implications for interpreting heat recirculation measurements.

Abstract

A new class of exoplanets is beginning to emerge: planets whose dayside atmospheres more closely resemble stellar atmospheres as most of their molecular constituents dissociate. The effects of the dissociation of these species will be varied and must be carefully accounted for. Here we take the first steps towards understanding the consequences of dissociation and recombination of molecular hydrogen (H$_2$) on atmospheric heat recirculation. Using a simple energy balance model with eastward winds, we demonstrate that H$_2$ dissociation/recombination can significantly increase the day$-$night heat transport on ultra-hot Jupiters (UHJs): gas giant exoplanets where significant H$_2$ dissociation occurs. The atomic hydrogen from the highly irradiated daysides of UHJs will transport some of the energy deposited on the dayside towards the nightside of the planet where the H atoms recombine into H$_2$; this mechanism bears similarities to latent heat. Given a fixed wind speed, this will act to increase the heat recirculation efficiency; alternatively, a measured heat recirculation efficiency will require slower wind speeds after accounting for H$_2$ dissociation/recombination.