A Dynamic Auroral Ionospheric Density Profile Reveals a Planetary-Scale Cavity at Jupiter

Low-altitude measurements above Jupiter’s main auroras have shown the presence of persistent auroral density depletions. This low density regime strongly favors auroral acceleration by inertial Alfvén waves to explain the predominance of energetic (100–1000 keV) broadband electron beams. Well-constrained auroral density measurements are central to describing the role of inertial Alfvén waves in auroral acceleration. Here we present a refined analysis of auroral electron density measurements in the diffuse and main auroral zones using magnetic field and particle data from the Juno spacecraft. We report densities within the upward current region (Zone-I) typically ranging from 10 -2 –10 -1 cm -3 , with depletions to order 10 -4 cm -3 . Downward current region (Zone-II) densities remain poorly constrained. We provide an improved electron density profile within a few degrees latitude of the auroral oval by accounting for auroral zone dynamics. These results support the presence of a persistent large-scale density cavity in Jupiter's polar regions.