High Latitude Zones of GeV Heavy Ions at the Inner Edge of Jupiter's Relativistic Electron Belt

Abstract

AbstractJuno has discovered signatures of a high energy heavy ion population (>100 MeV/nucleon) within the inner edge of Jupiter's relativistic electron belt. The particles were detected in narrow zones in the high‐latitude lobes of the synchrotron emission region, a location never explored by prior spacecraft (∼31°–46° magnetic latitude; radial distances 1.12–1.41 Jovian radii, M‐shells 1.5–2.37). The population was revealed by extremely high signal ionization signatures seen in images collected by Juno's Stellar Reference Unit star camera (equivalent to 0.2–0.7 MeV of deposited energy per pixel). Signature morphology indicates a population of GeV ions (Z > 1) with atomic mass as high as sulfur, although species with 2 ≤ Z ≤ 8 potentially account for all of the signatures. The detections have occurred while the spacecraft is magnetically connected to Jupiter's halo and gossamer rings, but not while it is connected to the main ring; similar to equatorial observations of GeV carbon and sulfur ions by the Galileo Probe. We find that the particles reside on magnetic drift shells that suggest they are stably trapped within Jupiter's magnetosphere. Because the cosmic ray albedo neutron decay mechanism can only produce protons and electrons, it cannot be the source of this trapped Z > 1 ion population; other galactic cosmic ray origins are suspected. Inward radial transport of tens of keV heavy ions from the outer magnetosphere is another potential source.