Ganymede's Radiation Cavity and Radiation Belts

While planetary radiation belts are all embedded within the low energy solar wind, Ganymede is in the unique situation of being surrounded by the energetic particles of Jupiter's magnetosphere. Here we study Ganymede's environment based the recent flyby of Juno, as well as through reanalysis of past measurements from the Galileo spacecraft. We find that Ganymede is surrounded by a radiation cavity with intensities that are lower compared to Jupiter. Particles are lost in the cavity due to absorption by Ganymede that is likely enhanced by scattering. In the core of the cavity we find radiation belts. Their intensities are comparable to Jupiter for ions but lower for electrons. The radiation belts form peaks in phase space density, which indicates that they cannot be produced through steady inward influx and accumulation of Jupiter particles. Other processes are needed such as local acceleration, or time dependent transport and loss processes.