Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetized hot Jupiters

TL;DR

This study models the interaction between stellar wind plasma and the upper atmosphere of non-magnetized hot Jupiters, revealing induced magnetic fields that influence the planetary obstacle's position and providing insights into the planets' magnetic properties.

Contribution

It introduces a 3D MHD model of stellar wind interaction with non-magnetized hot Jupiters, highlighting the formation of induced magnetic fields and their effects on planetary obstacle location.

Findings

Induced magnetic fields are stronger than those at Venus and Mars.

The planetary obstacle can be closer by up to 0.5-1 planetary radii due to induced fields.

HD 209458b likely has an intrinsic magnetic moment of 10-20% that of Jupiter.

Abstract

We investigate the interaction between the magnetized stellar wind plasma and the partially ionized hydrodynamic hydrogen outflow from the escaping upper atmosphere of non- or weakly magnetized hot Jupiters. We use the well-studied hot Jupiter HD 209458b as an example for similar exoplanets, assuming a negligible intrinsic magnetic moment. For this planet, the stellar wind plasma interaction forms an obstacle in the planet's upper atmosphere, in which the position of the magnetopause is determined by the condition of pressure balance between the stellar wind and the expanded atmosphere, heated by the stellar extreme ultraviolet (EUV) radiation. We show that the neutral atmospheric atoms penetrate into the region dominated by the stellar wind, where they are ionized by photo-ionization and charge exchange, and then mixed with the stellar wind flow. Using a 3D magnetohydrodynamic (MHD) model, we show that an induced magnetic field forms in front of the planetary obstacle, which appears to be much stronger compared to those produced by the solar wind interaction with Venus and Mars. Depending on the stellar wind parameters, because of the induced magnetic field, the planetary obstacle can move up to ~0.5-1 planetary radii closer to the planet. Finally, we discuss how estimations of the intrinsic magnetic moment of hot Jupiters can be inferred by coupling hydrodynamic upper planetary atmosphere and MHD stellar wind interaction models together with UV observations. In particular, we find that HD 209458b should likely have an intrinsic magnetic moment of 10-20% that of Jupiter.