Thermal Processes Governing Hot-Jupiter Radii

TL;DR

This paper investigates various heating mechanisms, including atmospheric, interior, and ohmic heating, and their effects on the radius evolution of hot Jupiters, emphasizing the importance of heat redistribution and cooling processes.

Contribution

It provides a comprehensive comparison of atmospheric and interior heating effects and assesses the role of ohmic heating in inflating hot Jupiters, incorporating realistic cooling and heat redistribution.

Findings

Models with day/night cooling resemble isotropic irradiation with increased heat redistribution.

Ohmic heating alone cannot cause runaway radius inflation.

Highly irradiated planets cannot sustain strong magnetic fields over large daysides.

Abstract

There have been many proposed explanations for the larger-than-expected radii of some transiting hot Jupiters, including either stellar or orbital energy deposition deep in the atmosphere or deep in the interior. In this paper, we explore the important influences on hot-Jupiter radius evolution of (i) additional heat sources in the high atmosphere, the deep atmosphere, and deep in the convective interior; (ii) consistent cooling of the deep interior through the planetary dayside, nightside, and poles; (iii) the degree of heat redistribution to the nightside; and (iv) the presence of an upper atmosphere absorber inferred to produce anomalously hot upper atmospheres and inversions in some close-in giant planets. In particular, we compare the radius expansion effects of atmospheric and deep-interior heating at the same power levels and derive the power required to achieve a given radius increase when night-side cooling is incorporated. We find that models that include consistent day/night cooling are more similar to isotropically irradiated models when there is more heat redistributed from the dayside to the nightside. In addition, we consider the efficacy of ohmic heating in the atmosphere and/or convective interior in inflating hot Jupiters. Among our conclusions are that (i) the most highly irradiated planets cannot stably have uB > (10 km/s Gauss) over a large fraction of their daysides, where u is the zonal wind speed and B is the dipolar magnetic field strength in the atmosphere, and (ii) that ohmic heating cannot in and of itself lead to a runaway in planet radius.