Interaction of a close-in extrasolar planet with the magnetic field of its host star

Abstract : The numerous and diverse extrasolar planets detected since 1995 provide much inspiration for planetary astrophysics. A fraction of these extrasolar planets orbit their host stars at semi-major axes less than 0.1 AU; a planet which has migrated toward its host star would thus first encounter a strong magnetized wind and, as it enters the stellar magnetosphere, strong magnetic fields. We model the interaction of such a close-in extrasolar planet with the dipolar magnetic field of its host star and study separately the time-dependent and independent components. The time-dependent interaction gives rise to Eddy currents confined in the planet. We investigate two effects that may transfer angular momentum to a planet approaching its host TTauri star through type II migration: a Lorentz torque that transfers angular momentum from the stellar spin to the planetary orbit and a mass loss induced by the ohmic dissipation in the planet, which may transfer angular momentum to the planet as the gas is accreted onto the star. We model the time-independent interaction with the unipolar inductor model, which allows the current induced in the planet to flow along a closed loop constituted by the planet, the flux tube, and its footprint on the stellar atmosphere. We self-consistently calculate the ohmic dissipation in the planet and the star and the associated Lorentz torque. We then suggest that the ohmic dissipation may provide the extra energy needed to explain some planets with inflated radii. Finally, we propose that the model may also be used to remotely infer the electric conductivity of the outer layers of super-Earths interacting magnetically with their host stars.
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Randy Olivier Laine. Interaction of a close-in extrasolar planet with the magnetic field of its host star. Other [cond-mat.other]. Université d'Orléans, 2013. English. ⟨NNT : 2013ORLE2021⟩. ⟨tel-01059808⟩



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