Energetic Proton Acceleration Associated With Io's Footprint Tail

Observations of energetic charged particles associated with Io's footprint (IFP) tail, and likely within or very near the Main Alfven Wing, during Juno's 12th perijove (PJ) crossing show evidence of intense proton acceleration by wave-particle heating. Measurements made by Juno/JEDI reveal proton characteristics that include pitch angle distributions concentrated along the upward loss cone, broad energy distributions that span similar to 50 keV to 1 MeV, highly structured temporal/spatial variations in the particle intensities, and energy fluxes as high as similar to 100 mW/m(2). Simultaneous measurements of the plasma waves and magnetic field suggest the presence of ion cyclotron waves and transverse Alfvenic fluctuations. We interpret the proton observations as upgoing conics likely accelerated via resonant interactions with ion cyclotron waves. These observations represent the first measurements of ion conics associated with moon-magnetosphere interactions, suggesting energetic ion acceleration plays a more important role in the IFP tail region than previously considered. Plain Language Summary NASA's Juno spacecraft orbits Jupiter's polar region and makes direct measurements of the fields and particles that are responsible for creating Jupiter's powerful auroras. In this article, we present new observations that show intense proton acceleration occurring at altitudes near the auroral emissions created by the interaction between Jupiter's moon Io and the surrounding plasma and magnetic field environment. These unique observations provide clues on how particles are being accelerated and will help constrain particle acceleration theories.