A heavy ion and proton radiation belt inside of Jupiter's rings

Abstract

Energetic charged particle measurements by the Jupiter Energetic Particle Detector Instrument (JEDI) on board Juno have revealed a radiation belt of hundreds of keV ions up to the atomic mass of sulfur, located between Jupiter's rings and atmosphere. Proton energy spectra display an unusual intensity increase above 300 keV. We suggest that this is because charge exchange in Jupiter's neutral environment does not efficiently remove ions at such high energies. Since this innermost belt includes heavy ions, it cannot be exclusively supplied by cosmic ray albedo neutron decay, which is an important source at Earth and Saturn but only supplies protons and electrons. We find indications that the stripping of energetic neutral atoms in Jupiter's high atmosphere might be the ion source. Since the stripped off electrons are of low energy, this hypothesis is consistent with observations of the ratio of energetic electrons to ions being much less than 1.

Plasma measurements in the Jovian polar region with Juno/JADE

“…To interpret these data, we have identified five distinct regions in the JADE heavy ion and electron data, which we posit physically map to the Io torus, inner plasma sheet, middle plasma sheet, outer plasma sheet, and the high-latitude polar region. We note that this work focuses on the lower energy plasma populations within the JADE energy range, where the energetic plasma populations are discussed in other studies in this issue Haggerty et al, 2017;Kollmann et al, 2017;Mauk et al, 2017]. In this study, high densities of electrons, oxygen, and sulfur and their variation with energy and intensity are used as discriminators between different magnetospheric and other regions.…”

Radiation near Jupiter detected by Juno/JEDI during PJ1 and PJ3

“…During these times, we have found that the >15 MeV electrons dominate the count rates with a smaller contribution (<40%) from 0.7 to 15 MeV electrons. Excluding the population right near perijove [ Kollmann et al , ], we did not find a strong contribution to the count rates in these high‐latitude regions from <700 keV electrons. Near the planet, hundreds of keV to 1 MeV protons measured by Juno are found to vary strongly with the exact position of the spacecraft.…”

“…The increase in Figure 3 (bottom) at~12:38 UTC suggests that energetic protons are contributors, but those channels are not sampled in the Geophysical Research Letters 10.1002/2017GL072600 high-voltage safing period (12:42 to 13:02 UTC). Kollmann et al [2017] examine these measurements in much greater detail.…”

Intervals of Intense Energetic Electron Beams Over Jupiter's Poles

“…In addition to the time-energy or time-pitch angle spectrograms, the ion SSD singles rates can also be useful for extracting information about the beams. For foreground particles in the tens to several hundreds of keV energy range, the singles rates are often organized as they are near 12:45 (Figure 1, fifth panel) at the position of a local maximum observed near Juno's closest approach to Jupiter (see Kollmann et al, 2017). The two witness-shielded detectors (SSD1 and SSD3) measure the lowest rates, and SSD0, which has some collimator blockage, measures a lower rate than the unobstructed detectors (SSD2, SSD4, and SSD5).…”