Simulating the Escaping Atmosphere of GJ 436 b with Two-fluid Magnetohydrodynamic Models

Abstract

Observations of transmission spectra reveal that hot Jupiters and Neptunes are likely to possess escaping atmospheres driven by stellar radiation. Numerous models predict that magnetic fields may exert significant influences on the atmospheres of hot planets. Generally, the escaping atmospheres are not entirely ionized, and magnetic fields only directly affect the escape of ionized components within them. Considering the chemical reactions between ionized components and neutral atoms, as well as collision processes, magnetic fields indirectly impact the escape of neutral atoms, thereby influencing the detection signals of planetary atmospheres in transmission spectra. In order to simulate this process, we developed a magneto-hydrodynamic multi-fluid model based on MHD code PLUTO. As an initial exploration, we investigated the impact of magnetic fields on the decoupling of H${}^{+}$ and H in the escaping atmosphere of the hot Neptune GJ436 b. Due to the strong resonant interactions between H and H${}^{+}$, the coupling between them is tight even if the magnetic field is strong. Of course, alternatively, our work also suggests that merging H and H${}^{+}$ into a single flow can be a reasonable assumption in MHD simulations of escaping atmospheres. However, our simulation results indicate that under the influence of magnetic fields, there are noticeable regional differences in the decoupling of H${}^{+}$ and H. With the increase of magnetic field strength, the degree of decoupling also increases. For heavier particles such as O, the decoupling between O and H${}^{+}$ is more pronounced. Our findings provide important insights for future studies on the decoupling processes of heavy atoms in the escaping atmospheres of hot Jupiters and hot Neptunes under the influence of magnetic fields.

References in corpus (22)

• PLUTO: a Numerical Code for Computational Astrophysics
• Atmospheric Escape from Hot Jupiters
• A giant comet-like cloud of hydrogen escaping the warm Neptune-mass exoplanet GJ 436b
• Lyman-$\alpha$ Transit Spectroscopy and the Neutral Hydrogen Tail of the Hot Neptune GJ436b
• Energetic neutral atoms as the explanation for the high velocity hydrogen around HD 209458b
• Exoplanet HD209458b: inflated hydrogen atmosphere but no sign of evaporation
• The long egress of GJ~436b's giant exosphere
• Hubble Space Telescope detection of oxygen in the atmosphere of exoplanet HD189733b
• Atmosphere Expansion and Mass Loss of Close-Orbit Giant Exoplanets heated by Stellar XUV. II. Effects of Planetary Magnetic Field, Structuring of inner Magnetosphere
• Atmospheric Regimes and Trends on Exoplanets and Brown Dwarfs
• Magnetohydrodynamic Simulations of Hot Jupiter Upper Atmospheres
• Escaping Particle fluxes in the atmospheres of close-in exoplanets: I. model of hydrogen
• Signatures of Strong Magnetization and Metal-Poor Atmosphere for a Neptune-Size Exoplanet
• Global 3D hydrodynamic modeling of in-transit Lyα absorption of GJ436b
• Re-visit of HST FUV observations of hot-Jupiter system HD 209458: No Si III detection and the need for COS transit observations
• Spectral, Spatial, and Time properties of the hydrogen nebula around exoplanet HD209458b
• Lyα Absorption at Transits of HD 209458b: A Comparative Study of Various Mechanisms Under Different Conditions
• The impact of intrinsic magnetic field on the absorption signatures of elements probing the upper atmosphere of HD209458b
• Global 3D simulation of the upper atmosphere of HD189733b and absorption in metastable HeI and Lyα lines
• Modeling H$\alpha$ and He 10830 transmission spectrum of WASP-52b
• Global 3D hydrodynamic modeling of absorption in Lyα and He 10830 A lines at transits of GJ3470b
• Mysterious non-detection of HeI (23S) transit absorption of GJ436b