An Overview of Juno's Close Encounter with Ganymede

On 7 June 2021 the Juno spacecraft passed Ganymede at an altitude of 1046 km. The orientation of Juno's elliptical polar orbit around Jupiter has been evolving due to Jupiter's oblateness, with apojove moving southward, and now the inbound leg of the trajectory is crossing Jupiter's equatorial plane at the distance of the galilean satellites. The Juno payload, designed to probe Jupiter's magnetosphere with a comprehensive complement of fields and particles instruments, was also ideal for studying Ganymede's unique mini-magnetosphere. The spacecraft approached Ganymede from the night side, went behind Ganymede as seen from the earth (achieving an earth occultation), passed through the moon's magnetosphere, and then departed on the sunlit ~sub-jovian side. Juno's probe of Ganymede's magnetosphere gave us new details on the composition of the ions and the electron density, and showed a day-night asymmetry in the electron density profile. Mapping the ultraviolet emissions at the edge of the closed field lines to the structure of the magnetosphere has turned out to be surprisingly challenging. Juno's remote sensing instruments collected new data in the visible and near-infrared, and, for the first time, mapped the surface and subsurface with 6 microwave channels. Remote sensing of Ganymede returned new results on geology, surface composition and thermal properties of the surface and subsurface. The orientation of Juno's orbit continues to evolve, enabling close passes of Europa in September 2022 and Io in 2023 and 2024.