New understanding on wave-particle interactions over Jupiter's polar auroras as revealed by Juno

Since its arrival at Jupiter on 5 July, 2016, the Juno spacecraft has observed Jupiter's polar magnetosphere from its unique polar orbit. Juno has a suite of magnetospheric instruments onboard, including in situ wave, particle, and field detectors. Three kinds of waves recorded by these instruments are related to wave-particle interactions over the polar auroras at Jupiter. The first kind is composed of broadband Alfvénic waves at frequencies below 5 Hz. These waves are present over the main auroral oval and Io footprint tails, contributing to stochastic acceleration of the particles precipitating onto the atmosphere. The second kind consists of whistler-mode waves at frequencies below 20 kHz. These waves are frequently accompanied by energetic precipitating electrons in the polar cap and main auroral oval regions and by low-energy electrons along the magnetic field lines connected to Io's footprint tails. Hence, broadband Alfvénic waves and whistler-mode waves appear to play essential roles in Jupiter's auroras. At radio frequencies up to 40 MHz, the third kind of waves are auroral radio waves distributed along auroral magnetic field lines at emission frequencies very close to the local cyclotron frequency via the electron cyclotron maser instability (CMI). Juno's observations indicate that unstable electron distributions that drive CMI are either loss-cone or conic type, and the low-frequency radio component is tied to the main auroral oval. In this presentation, we report an overview of the recent observations and theoretical considerations of three kinds of waves related to auroral phenomena at Jupiter as revealed by Juno. Also, these findings would be a benchmark to understand wave-particle interactions near Jovian moons for future exploration missions.