Energetic particle measurements near Ganymede: Galileo EPD data revisited and perspectives for Juice PEP

The Galileo spacecraft performed close flybys of the moon Ganymede between 1996 and 2001. We reanalysed data of the energetic particles detector EPD onboard Galileo and derived the particle fluxes, energy spectra, and pitch angle distributions in the energy range of several keV to MeV during Ganymede flybys G2, G7, G8, G28, and G29. We find sharp dropouts in ion and electron fluxes as signatures of the loss cones inside the Ganymede magnetosphere as well as trapped electron distribution. Additionally, bi-directional field-aligned and butterfly distributions were found as well. We discuss these findings compared with simulation results in charactering Ganymede’s magnetosphere and in the context of future measurements with the Particle Environment Package PEP onboard the Juice mission which will be in orbit around Ganymede in 2032.