Using Ion Injections to Infer the Energetic Oxygen and Sulfur Charge States in Jupiter’s Inner and Middle Magnetosphere

Abstract:

Neutral gases can, through the charge exchange processes, shape the distributions of energetic ions trapped within a planetary magnetosphere, and also redistribute the energetic ion charge states. One region where the prevalence of such processes has been proposed is the orbital region of Jupiter’s moon Europa, where the existence of a neutral gas torus has been inferred. Data from the Galileo Energetic Particle Detector (EPD) showed a depletion of protons with near equatorial pitch angles near Europa, while oxygen and sulfur maintained their trapped profile as they were transported inward. The contrast in these distributions was attributed by Lagg et al. (2003) to the multiple charge states of the oxygen and sulfur, dramatically increasing the charge exchange lifetimes of these species. It was proposed that as the ions diffuse inwards across Europa’s orbit and into the Io torus regions, the distributed neutral gas interactions redistribute the charge states of the heavy ions until, close to Io, these ions may be heavily depleted. And so, the charge state of the heavy ions is a critical parameter in determining whether or not these processes are taking place. Limited evidence for the multiple charged states of heavy ions was provided by Mauk et al. [1999], who analyzed three ion injection events and found evidence of multiply charged energetic oxygen and sulfur ions in two of the events, but not in the third event. Injections introduce a transient disturbance to the ion distributions, and the drift rate of disturbed ions away from the injection region depends on the charge state of the ions. In this work we revisit the Galileo EPD data set and find additional ion dispersion events from which composition can be measured and charge state can be inferred. We aspire to develop a much clearer picture as to the ordering of charge state as a function of radial distance. Results and conclusions will be presented as well as the importance from new measurements from the upcoming Juno, JUICE, and Europa missions.