Effect of stellar wind induced magnetic fields on planetary obstacles of non-magnetised hot Jupiter's
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.