Proton Equatorial Pitch Angle Distributions in Jupiter's Inner Magnetosphere

We use data from the plasma and energetic particle instruments on the Juno spacecraft, JADE and JEDI, to study the equatorial pitch angle distributions of energetic protons within Jupiter's inner magnetosphere during Juno's prime mission from 2016 to 2021. Averaging over all observations made by Juno within M-shell bins between M = 6 and M = 30, we find protons at energies between 10 and 50 keV are predominantly field-aligned at all M-shells. In contrast, those at energies above 200 keV transition from being predominantly field-aligned at M = 20 to having pancake-like distributions at M < 10. We find the observed distributions are consistent either with charge exchange of protons with neutral toroidal clouds, or with adiabatic acceleration of protons originating from Jupiter that are transported inward from the middle magnetosphere.