The spatial structure and temporal variability of Ganymede’s auroral ovals from Hubble Space Telescope observations

Abstract

We investigate properties of Ganymede’s FUV auroral ovals using spectral images acquired during the past two decades with Hubble’s Space Telescope Imaging Spectrograph (HST/STIS). The observations cover Ganymede at eastern and western elongation. We analyze the variability of the structure and brightness of the auroral ovals as a function of magnetic latitude. The investigation of the aurora is a diagnostic tool of the various processes, which contribute to Ganymede’s complex magnetic field environment. The variability which we find consists of both, spatial inhomogeneities on the moon disk and temporal variation as a function of Ganymede’s position within the current sheet of Jupiter’s magnetosphere. An additional temporal variability is present as the brightness properties vary for different elongations in different periods.