Field-aligned proton beams are a systematic and identifiable feature associated with Jupiter's auroral emissions, transporting 3 ± 2 kg s−1 away from Jupiter's ionosphere. This mass loss occurs at all longitudes sampled by Juno around the southern auroral oval, while the northern hemisphere exhibits upward proton beams predominantly on one portion in System III, near the auroral kink region. These beams are associated with upward inverted-V structures indicative of quasi-static magnetic field- aligned parallel potentials. A lack of bidirectionality indicates these proton populations are pitch-angle and/or energy scattered and incorporated into the magnetospheric charged particle environment. This mechanism is a significant, and potentially dominant, source of protons in Jupiter's middle and outer magnetosphere. If Jupiter's ionosphere is the primary source for protons in the inner magnetosphere, they are likely sourced equatorward of the main emissions and at energies <100 eV.
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