Revisiting Discrete Energy Bands in Galilean Moon's Footprint Tails: Remote Signals of Particle Absorption

Observations from the Juno spacecraft near the M-shells of the Galilean moons have identified alternating enhancements and reductions of particle fluxes at discrete energies. These banded structures were previously attributed to bounce resonance between particles and standing Alfvén waves generated by moon-magnetospheric interactions. Here, we show that this explanation is inconsistent with key observational features, and propose an alternative interpretation: the bands are remote signatures of particle absorption at the moons. In this scenario, whether a particle encounters the moon before reaching Juno depends on the number of bounce cycles it undergoes within a fixed drift segment determined by the moon-spacecraft separation. Therefore, the absorption bands are expected to appear at discrete, equally-spaced velocities. This is largely consistent with the observations, though discrepancies remain, possibly due to spacecraft charging and/or finite data resolution. This finding improves our understanding of moon-plasma interactions and may help constrain Jovian magnetospheric models.