Modeling the Dynamics and Thermochemistry for the Outer Atmospheres of the Ultra-hot Jupiter WASP-121b

TL;DR

This paper presents advanced 3D simulations of the ultra-hot Jupiter WASP-121b, revealing complex atmospheric dynamics, outflow structures, and spectral features that match observations and improve understanding of such exoplanets.

Contribution

The study introduces comprehensive 3D coupled hydrodynamics and thermochemistry simulations of WASP-121b, capturing detailed atmospheric layers and outflow morphologies influenced by stellar irradiation and wind effects.

Findings

Spiral arm velocities reach ~40 km/s, explaining high-velocity absorption features.

Enhanced FUV irradiation intensifies outflows and extends spiral structures.

Stellar wind confinement affects outflow compression and helium absorption.

Abstract

We present three-dimensional simulations of the ultra-hot Jupiter (UHJ) WASP-121b from the planetary surface to extended outflows, coupling hydrodynamics with consistent non-equilibrium thermochemistry, ray-tracing radiative transfer, and hydrodynamics using the GPU-accelerated Kratos framework. The fiducial model exhibits several atmospheric layers, including the lower atmospheres controlled by day-night circulation, and transonic photoevaporative outflows at higher altitudes shaped into two spiral arms by the stellar gravity and orbital motion effects. Different species could trace different regions: Fe probes rotation-dominated inner layers, Na maps dense spiral arms where recombination balances photoionization, and H$\alpha$ and He $10830~{\rm A}$ features trace progressively more extended, ionized gas. With spiral arm velocities reaching $\sim 40~{\rm km\ s}^{-1}$ projected along the line of sight, this morphology explains observed high-velocity Na and H$\alpha$ absorption features without requiring significant super-rotation jet streams. Parametric studies reveal complex dependencies on stellar irradiation: enhanced FUV intensifies outflows and extends spiral arms spatially and kinematically, while EUV and X-ray expands spiral structures into attenuated, ionized regions. Stellar wind confinement compresses the dayside outflow and enhances metastable helium absorption. This work demonstrates that current and future transmission spectral observations that probe multiple species can provide important constraints on astrophysical environments of UHJs by comparing state-of-the-art simulations.