Hot Jupiters are Inflated Primarily by Shallow Heating

TL;DR

This study suggests that shallow heating near the radiative-convective boundary, rather than deep interior heating, primarily causes the inflated radii of hot Jupiters, supported by thermal evolution modeling and Bayesian analysis.

Contribution

It introduces a thermal evolution model with a parameter for shallow heating and demonstrates that shallow heating explains hot Jupiter inflation better than deep heating models.

Findings

Hot Jupiters' cooling rates are reduced by 95-98% compared to simple models.

Shallow heating near radiative-convective boundaries is the most plausible inflation mechanism.

Atmospheric circulation observables should vary with equilibrium temperature as predicted.

Abstract

The unexpectedly large radii of transiting hot Jupiters have led to many proposals for the physical mechanisms responsible for heating their interiors. While it has been shown that hot Jupiters reinflate as their host stars brighten due to heating deep in planetary interiors, young hot Jupiters also exhibit signs of delayed cooling possibly related to heating closer to their surfaces. To investigate this ambiguity, we enhance our previously published hot Jupiter thermal evolution model by adding a parameter that allows for both deep heating and delayed cooling. We fit our thermal evolution models to a homogeneous, physically self-consistent catalog of accurate and precise hot Jupiter system properties in a hierarchical Bayesian framework. We find that hot Jupiters' interior cooling rates are reduced on average by 95\%--98\% compared to simpler anomalous heating models. The most plausible explanation for this inference is substantial shallow heating just below their radiative--convective boundaries that enables reinflation with much weaker deep heating. Shallow heating by Ohmic dissipation and/or temperature advection are therefore important components of accurate models of hot Jupiter atmospheres, especially in circulation models. If hot Jupiters are inflated primarily by shallow heating as we propose, then we predict that atmospheric circulation-related observables should increase with temperature in the range $T_{\text{eq}}~\lesssim1500~\text{K}$, peak in the range $1500~\text{K}~\lesssim~T_{\text{eq}}~\lesssim~1800~\text{K}$, and decrease in the range $T_{\text{eq}}~\gtrsim~1800~\text{K}$.