The fluxes and phase space densities for a fixed 1st adiabatic invariant for high energy electrons and protons provide important inputs for various scientific studies for determining the physics of particle diffusion and energization. This study provides estimates of the 1st adiabatic invariant and phase space density based on the complete and large data base available from the Energetic Particle Detector (EPD) on Galileo for the jovian environment. To be specific, 10 minute averages of the high energy electron and proton data are used to compute differential flux spectra versus energy for L=~8 - 25 over the Galileo mission. These spectra provide estimates of the differential fluxes and phase space density for constant 1st adiabatic invariants between 102 to 105 MeV/G. As would be expected, the electron and proton fluxes and phase space densities generally trend lower as the planet is approached. The results indicate that, whereas the overall trends for each orbit are consistent, detailed orbit to orbit variations can be observed. Galileo orbit C22 is presented as a specific example of deviations from the mean downward trend. To validate the Galileo results and extend the findings into L=3, the GIRE3 model was also used to compute the fluxes and phase space densities for constant 1st adiabatic invariant versus L-shell. Comparison between GIRE3 and EPD demonstrates that the model adequately reproduces the EPD data trends and they consistently show additional variations near Io. This provides proof that the GIRE3 is a useful starting point for diffusion analyses and similar studies.

Jupiter is surrounded by intense and energetic radiation belts, yet most of the available in-situ data, in volume and quality, were taken outside of Europa’s orbit, where radiation conditions are not that extreme. Here we study measurements of ions of tens of keV to tens of MeV at <10 Jupiter radii (RJ) distance to Jupiter, therefore inward of the orbit of Europa. Ion intensities drop around 6RJ, near Io’s orbit. Previous missions reported on radiation belts of tens and hundreds of MeV ions located between 2 and 4 RJ. Measurements of lower energies were not conclusive because high energy particles typically contaminate the measurement of lower energy particles. Here we show for the first time that ions in the hundreds of keV range are present and suggest that ions may extend even into the GeV range. The observation of charged particles yields information on the entire field line, not just the local field. We find that there is a region close to Jupiter where no magnetic trapping is possible. Jupiter’s innermost radiation belt is located at <2RJ, inward of the main ring. Previous work suggested that this belt is sourced by reionized energetic neutral atoms coming steadily inward from distant regions. Here we perform a phase space density analysis that shows consistency with such a local source. However, an alternative explanation is that the radiation belt is populated by occasional strong radial transport and then decays on the timescale of years.