Hot Spot Offset Variability from Magnetohydrodynamical Thermoresistive Instability in Hot Jupiters

Abstract

Hot Jupiter atmospheres are possibly subject to a thermoresistive instability. Such an instability may develop as the ohmic heating increases the electrical conductivity in a positive feedback loop, which ultimately leads to a runaway of the atmospheric temperature. We extend our previous axisymmetric one-dimensional radial model, by representing the temperature and magnetic diffusivity as a first order Fourier expansion in longitude. This allows us to predict the hot spot offset during the unfolding of the thermoresistive instability and following Alfvénic oscillations. We show a representative simulation undergoing the thermoresistive instability, in which the peak flux offset varies between approximately $\pm 60^{\circ}$ on timescales of a few days with potentially observable brightness variations. Therefore, this thermoresistive instability could be an observable feature of hot Jupiters, given the right timing of observation and transit and the right planetary parameters.