Jupiter’s radiation belts as a target for NASA’s Heliophysics Division

NASA's Heliophysics division studies "the Sun, the heliosphere, and Earth's magnetosphere and... universal plasma phenomena".We argue that Jupiter's radiation belts, magnetosphere, and near-space environment should be considered as relevant targets for NASA's Heliophysics missions.All universal processes called out in the previous Decadal study can be found around Jupiter.Such physics is much more relevant and directly maps to the defined focus of NASA's Heliophysics division than to the core sciences of NASA's Planetary Sciences division.Jupiter's magnetosphere is an environment of extremes: of all the planets in the solar system it is the largest natural particle accelerator, has the strongest magnetic field, the fastest spin, and the most geologically active moon that provides plasma to the magnetosphere.While the intensities of ultrarelativistic electrons with energies in excess of several MeV at Earth become significant only during the most rare and extreme events, electron acceleration to many tens of MeV occurs at Jupiter all the time.Even relativistic heavy ions such as oxygen and sulfur can be trapped up to tens of GeV.All this makes Jupiter ideal to particularly study the fundamentals of particle acceleration.At the same time, it also provides a unique opportunity to study the potential extremes of terrestrial space weather.While the waves driving acceleration processes at Earth are found throughout the L-shells of the radiation belts, at Jupiter they are limited to more discrete and narrow ranges, making it easier to disentangle local from non-local acceleration.While energetic particle dynamics at Earth's magnetosphere are in part driven by magnetopause shadowing and substorms, Jupiter's belts are embedded so deep within the magnetosphere that these effects are thought to be negligible: the outer magnetosphere is instead a huge reservoir for pre-accelerating radiation belt particles.