JEDI overview of Juno’s first close Ganymede flyby

On 7 June 2021, the Juno spacecraft made its first close flyby of Jupiter’s largest moon—Ganymede—at an altitude of ~1045 km. Additionally, this is the first spacecraft encounter with Ganymede’s space environment since the Galileo spacecraft over two decades earlier. Juno is equipped with an energetic particle instrument suite that is comprised of three sensors for optimal angular coverage on a sub-spacecraft spin basis. Here we report measurements from Juno’s Jupiter Energetic particle Detector Instrument or JEDI for short. Energetic particle observations associated with Ganymede’s magnetosphere depict the following: 1) a dynamic and structured transition between Jupiter’s environment to Ganymede’s magnetosphere; 2) evidence for precipitation onto Ganymede’s surface within the open field line region as a possible consequence of wave-particle interactions; 3) empty upward loss cones indicative of strong absorption by Ganymede’s surface; and 4) a radiation cavity around Ganymede where intensities are smaller compared to the Jovian environment.