Simulated Photoevaporative Mass Loss from Hot Jupiters in 3D

TL;DR

This study uses 3D hydrodynamic simulations to analyze asymmetric photoevaporative mass loss from hot Jupiters, revealing complex outflow structures and potential observable signatures like Lyman-alpha absorption.

Contribution

It introduces the first 3D models of hot Jupiter atmospheric escape that incorporate asymmetric stellar irradiation and ionization effects, advancing beyond previous 1D approaches.

Findings

Asymmetric outflow structures with neutral shadows on the nightside.

Steady-state mass loss rate of approximately 2×10^{10} g/s under solar-like UV flux.

Good agreement of 3D results with earlier 1D models for total mass loss and outflow features.

Abstract

Ionizing stellar photons heat the upper regions of planetary atmospheres, driving atmospheric mass loss. Gas escaping from several hot, hydrogen-rich planets has been detected using UV and X-ray transmission spectroscopy. Because these planets are tidally locked, and thus asymmetrically irradiated, escaping gas is unlikely to be spherically symmetric. In this paper, we focus on the effects of asymmetric heating on local outflow structure. We use the Athena code for hydrodynamics to produce 3D simulations of hot Jupiter mass loss that jointly model wind launching and stellar heating via photoionization. Our fiducial planet is an inflated, hot Jupiter with radius $R_p=2.14 R_{\rm Jup}$ and mass $M_p = 0.53 M_{\rm Jup}$. We irradiate the initially neutral, atomic hydrogen atmosphere with 13.6 eV photons and compute the outflow's ionization structure. There are clear asymmetries in the atmospheric outflow, including a neutral shadow on the planet's nightside. Given an incident ionizing UV flux comparable to that of the Sun, we find a steady-state mass loss rate of ~$2\times10^{10}$ g s$^{-1}$. The total mass loss rate and the outflow substructure along the substellar ray show good agreement with earlier 1D models, for two different fluxes. Our 3D data cube can be used to generate the outflow's extinction spectrum during transit. As a proof of concept, we find absorption of stellar Lyman-alpha at Doppler-shifted velocities of up to $\pm 50$ km s$^{-1}$. Our work provides a starting point for further 3D models that can be used to predict observable signatures of hot Jupiter mass loss.