HST observations of Ganymede for Junos PJ34 flyby

We report results from Hubble Space Telescope (HST) observations that were taken contemporaneously with the in-situ and remote-sensing measurements of the Juno spacecraft during its only close flyby at Ganymede on June 6, 2021, in order to help better understand the processes that are responsible for Ganymedes auroral emission. HST using the STIS ultraviolet spectrometer monitored Ganymedes UV emission on its orbitally trailing side around the time of Junos flyby of the satellite close to its 34th perijove (PJ34). The observations consist of six HST visits with a duration of approximately 40 minutes each. The campaign was split into three visits prior to the Juno flyby to monitor the state of the auroral emission before the flyby and into three HST orbits after to monitor changes in the aurora following the flyby. All exposures were carried out successfully. The data show oval bands and auroral structures at high planetocentric latitudes on Ganymede. The emission is highly time-variable, suggesting that dynamical processes operate in Ganymedes magnetosphere.