Revisit of discrete energy bands in Galilean moon's footprint tails: remote signals of particle absorption

TL;DR

This paper reexamines discrete energy bands observed near Galilean moons, proposing that these are signals of particle absorption rather than bounce resonance, thus enhancing understanding of moon-magnetosphere interactions.

Contribution

It challenges previous bounce resonance hypotheses and introduces an absorption-based interpretation consistent with observed energy band structures.

Findings

Absorption bands appear at discrete, equally-spaced velocities.

The new model aligns with observed particle flux enhancements.

Provides a method to evaluate Jovian magnetospheric models.

Abstract

Recent observations from the Juno spacecraft during its transit over flux tubes of the Galilean moons have identified sharp enhancements of particle fluxes at discrete energies. These banded structures have been suspected to originate from a bounce resonance between particles and standing Alfven waves generated by the moon-magnetospheric interaction. Here, we show that predictions from the above hypothesis are inconsistent with the observations, and propose an alternative interpretation that the banded structures are remote signals of particle absorption at the moons. In this scenario, whether a particle would encounter the moon before reaching Juno depends on the number of bounce cycles it experiences within a fixed section of drift motion determined by moon-spacecraft longitudinal separation. Therefore, the absorption bands are expected to appear at discrete, equally-spaced velocities consistent with the observations. This finding improves our understanding of moon-plasma interactions and provides a potential way to evaluate the Jovian magnetospheric models.