Profiling the Jovian ring system

The Magnetometer investigation’s Advanced Stellar Compass (ASC) onboard Juno provides the first ever in-situ measurements of energetic radiation in the region dominated by the Jovian ring system. The ASC cameras are efficient high energy charged particle detectors, sensitive to energetic electrons (>15MeV) and protons (>120MeV) penetrating the camera’s radiation shielding. A compilation of ASC radiation observations obtained (at 4 samples/s) subsequent to Juno’s arrival at Jupiter thus generated the first detailed map of these particles trapped in Jupiter’s magnetic field. Juno’s orbital evolution, dominated by the southward rotation of its line of apsides by about 1 degree per orbit ensures that practically all regions of Jupiter’s radiation belts are mapped. In the later orbits this drift brought Juno’s orbit to traverse the space near Jupiter connecting along magnetic field lines to the Jovian ring system. The faint, thin ring system of Jupiter occupies the equator between the minor moons Thebe and Methis, and an even fainter toroidal shaped halo inside Methis. The faint rings are predominantly made from micrometer-sized dust and the halo by submicrometer dust, and have resisted precise optical profiling of the rings. Energetic electrons trapped in drift shells meander inwards causing a slow scan of the entire ring region. By mapping the variation in the measured energetic particle flux connecting to the ring region, and comparing these to the undisturbed flux, a detailed profile of the dust rings and the halo is achieved. We present a detained radiation map of the dust ring region, and discuss implications for the density and distribution of ring and halo particulates.