Charge states of energetic ions in Jupiter’s radiation belt inferred from absorption microsignatures of Io

Abstract

The Heavy Ion Counter on the Galileo Jupiter orbiter observed depletions of energetic (≳5 MeV/nucleon) oxygen and sulfur ions near Io that are interpreted as absorption microsignatures. The two elements were equally abundant in this region of Jupiter’s radiation belt. Numerical simulations of microsignatures from Galileo orbits 27, 31, and 32, based on calculations of ion trajectories in models of the magnetospheric and Alfvén wing magnetic fields, show that the data are most consistent with the ions being fully ionized or nearly so. The conclusion is independent of field model inaccuracies, which cause some discrepancy between simulations and data, because the Alfvén wing field significantly deflects only those trajectories with relatively small gyroradii.