Two regimes of interaction of a Hot Jupiter's escaping atmosphere with the stellar wind and generation of energized atomic hydrogen corona

TL;DR

This study models the interaction between a Hot Jupiter's escaping atmosphere and stellar wind, revealing two distinct regimes that influence the formation of energized hydrogen clouds and their observational signatures.

Contribution

It introduces a 2D hydrodynamic model that captures two interaction regimes and details the formation of energetic neutral atom clouds around the planet.

Findings

Identifies two regimes: 'captured by the star' and 'blown by the wind'.

Describes the shape and location of energized hydrogen clouds.

Provides insights for interpreting Lyα transit spectra.

Abstract

The interaction of escaping upper atmosphere of a hydrogen rich non-magnetized analog of HD209458b with a stellar wind of its host G-type star at different orbital distances is simulated with a 2D axisymmetric multi-fluid hydrodynamic model. A realistic sun-like spectrum of XUV radiation which ionizes and heats the planetary atmosphere, hydrogen photo-chemistry, as well as stellar-planetary tidal interaction are taken into account to generate self-consistently an atmospheric hydrodynamic outflow. Two different regimes of the planetary and stellar winds interaction have been modelled. These are: 1) the "captured by the star" regime, when the tidal force and pressure gradient drive the planetary material beyond the Roche lobe towards the star, and 2) the "blown by the wind" regime, when sufficiently strong stellar wind confines the escaping planetary atmosphere and channels it into the tail. The model simulates in details the hydrodynamic interaction between the planetary atoms, protons and the stellar wind, as well as the production of energetic neutral atoms (ENAs) around the planet due to charge-exchange between planetary atoms and stellar protons. The revealed location and shape of the ENA cloud either as a paraboloid shell between ionopause and bowshock (for the "blown by the wind" regime), or a turbulent layer at the contact boundary between the planetary stream and stellar wind (for the "captured by the star" regime) are of importance for the interpretation of Ly{\alpha} absorption features in exoplanetary transit spectra and characterization of the plasma environments.