A Persistent Depletion of Plasma Ions Within Jupiter's Auroral Polar Caps

Abstract

AbstractRegions poleward of Jupiter's main auroral ovals are largely devoid of 0.01 to 46 keV/q ions. We report ion measurements from the plasma instrument on the Juno spacecraft in polar orbit around Jupiter that characterize the presence or absence of structured ion fluxes poleward of the main ovals. We approximate geometric centers of published north and south Jovian main ovals and develop a probability metric for observation of plasma ions as a function of angular distance from these centers to the magnetic foot points of the observations, in the north and south separately. Using data from Juno's first 26 perijoves, at Jovicentric distances of 1.06 to 12 RJ, this metric shows a systematic decrease within both north and south main ovals, in the probability of observing plasma ions as the chosen centers are approached. This is consistent with previous reports of large electrostatic potential drops above Jupiter's polar caps.