Magnetic winding and turbulence in ultra-hot Jupiters

Abstract

ABSTRACT While magnetism in exoplanets remains largely unknown, hot Jupiters have been considered as natural candidates to harbour intense magnetic fields, both due to their large masses, which might empower a larger internal dynamo, and, possibly, due to their high energy budgets coming from irradiation. In this work, we focus on the latter aspect and perform MHD simulations of a narrow dayside atmospheric column of ultra-hot Jupiters, suitable for very high local temperatures (T ≳ 3000 K). Due to the high conductivity in this regime, the primary influence is the winding of the magnetic field caused by the intense zonal winds. In our study, we include a forcing that mimics the wind profiles observed in GCMs near the substellar point. As a result, the shear layer generates a toroidal magnetic field, locally reaching a few kG, which is supported by meridional currents. Such fields and the sustaining currents do not depend on the internal field but are all confined in the thin (less than a scale-height) shear layer around 1 bar. Additionally, we add random perturbations that induce turbulent motions, which lead to further (but much smaller) magnetic field generation to a broader range of depths. These results enable the assessment of the atmospheric currents that are induced. Although here we use ideal MHD and the only resistivity comes from the numerical scheme at a fixed resolution, we estimate a posteriori the amount of Ohmic heat deposited in the outer layers, which could be employed in evolutionary models for Hot Jupiters’ inflated radii.