Energetic ion composition and acceleration mechanisms in the magnetosphere of Jupiter

Abstract

Based on the first 15 orbits of the Galileo spacecraft the composition of the energetic ion population of the Jovian magnetosphere has been studied for the first time on a global scale. More specific, three different types of ions are investigated: helium as the tracer of the solar wind, sulfur and oxygen to a large extent as tracers of the internal source Io and protons with a mixed origin from the solar wind, Jovian atmosphere/ionosphere and the Europa gas torus. The ion energy spectrum fundamental for the study of the ion composition is investigated and a characteristic shape is established as a distinct feature of the Jovian magnetosphere. Based on the observed ion energy spectra the relative ion abundance ratios of S/O, S/He, O/He and p/He at a specific energy/nucleon are derived and global maps are constructed. The global coverage of the Galileo trajectories enables a quantitative comparison with results of previous flyby missions for the same radial distance and local time. The large discrepancies derived from the comparison with the Voyager 2 results are attributed to temporal variations and to a strong energy dependence of the ion abundance ratios associated with the energy spectral shapes ...