Juno Measurements of Jupiter’s Magnetic Field and Innermost Radiation Belts

The Juno spacecraft continues to map the gas giant’s complex magnetic field and particle environment, taking advantage of the natural evolution of Juno’s polar orbit. Juno’s first orbits had perijoves just northward of the equator. With each subsequent orbit, Juno’s perijove marches northward by ∼1°, owing to the apsidal precession of the orbit caused by Jupiter’s tidal bulge. As Juno’s periJove migrated further northward in EM1 (through orbit 76) and EM2, the spacecraft began sampling (via particle counts in the MAG investigation camera head units, or CHUs) a population of very energetic (>20 Mev) particles with pitch angles greater than 50 degrees both inbound and outbound from perijove at a particular M-shell defined by an equatorial magnetic field minimum ~ 0.35 Gauss. It is the most challenging radiation environment encountered thus far by the Juno spacecraft, with implications for spacecraft and instrument operations as well as magnetospheric dynamics and electromagnetic radiation. This population crosses the Jovigraphic equator at radii between 2.15 and 2.39 Rj, a region of space occupied by the Thebe Gossamer ring (~1.8 – 3.1 Rj), motivating speculation regarding pitch angle scattering of inward diffusing particles by electrically charged dust.