A heavy ion and proton radiation belt inside of Jupiter's rings

Energetic charged particle measurements by the Jupiter Energetic Particle Detector Instrument (JEDI) on board Juno have revealed a radiation belt of hundreds of keV ions up to the atomic mass of sulfur, located between Jupiter's rings and atmosphere. Proton energy spectra display an unusual intensity increase above 300 keV. We suggest that this is because charge exchange in Jupiter's neutral environment does not efficiently remove ions at such high energies. Since this innermost belt includes heavy ions, it cannot be exclusively supplied by cosmic ray albedo neutron decay, which is an important source at Earth and Saturn but only supplies protons and electrons. We find indications that the stripping of energetic neutral atoms in Jupiter's high atmosphere might be the ion source. Since the stripped off electrons are of low energy, this hypothesis is consistent with observations of the ratio of energetic electrons to ions being much less than 1.