Particle Acceleration by Io’s Alfvénic Interaction (Invited)

The Juno spacecraft crossed flux tubes connected to the Io footprint tail at a range of latitudes and altitudes. The Jovian Auroral Distributions Experiment (JADE) instrument onboard Juno made observations of accelerated electrons and protons connected to the Io footprint tail aurora. JADE observed planetward electron energy fluxes of ~70 mW/m2 near the Io footprint, and ~10 mW/m2 farther down the tail, along with correlated, intense electric and magnetic wave signatures which also decreased in amplitude down the tail. All observed electron distributions were broad in energy, suggesting a dominantly broadband acceleration process, and did not show any inverted-V structure that would be indicative of acceleration by a quasi-static, discrete, parallel electric potential.Juno observed fine structure on scales of ~10s km, and confirmed independently with electron and wave measurements that a bifurcated tail can intermittently exist. Additionally, we report measurements that suggest proton acceleration is driven by Io’s Alfvénic interaction. While connected to Io’s footprint tail, JADE observed multiple proton populations accelerated in different magnetospheric locations, as well as a bifurcated proton tail structure. We will present these electron and proton observations and discuss how they fit into our evolving understanding of Io’s interaction with the Jovian magnetosphere.