Energetic heavy ions in Jupiter's nightside inner and middle magnetosphere: Juno/JEDI statistics

Jupiter's magnetosphere is dominated by heavy ions, mainly comprised of singly charged oxygen ions and doubly charged sulfur ions, rather than by protons as in the case of Earth's magnetosphere. We investigate the energy and spatial distributions of energetic heavy ions in Jupiter's nightside inner magnetosphere near the equatorial plane. We conducted a statistical survey of Juno/JEDI observations obtained during Juno's primary and extended mission phases, covering radial distances of approximately 5-30 Jupiter radii, local times of 18--24(00)--06 hours, and energies of about 0.1--10 MeV. The energy spectra can be approximately described by power laws. On average, the duskside observations show higher absolute fluxes and smaller spectral indices than the dawnside and midnightside observations, suggesting that heavy ions are generally more energetic in the dusk sector. At a fixed local time, the spectral indices decrease with decreasing M-shells inside about 20 Jupiter radii. Outside this radial range, however, the spectral indices exhibit a peak or plateau-like profile. The transition in heavy-ion dynamics is further reflected in the phase space density at fixed magnetic moment. It remains approximately constant outside 20 Jupiter radii, but decreases inside this distance, with the transition occurring at smaller M-shells for lower magnetic moments. The observations suggest a transition in the behavior of energetic heavy ions at ∼20 Jupiter radii. We find that non-adiabatic mechanisms are required to fully account for their spectral and spatial properties.