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

Abstract

We investigate properties of Ganymede’s OI 1356 Å and OI 1304 Å auroral ovals using spectral images acquired during the past two decades with Hubble’s Space Telescope Imaging Spectrograph (HST/STIS). The observations cover the leading and trailing side of Ganymede. We analyze the spatial and temporal variability of the brightness and the structure of the auroral ovals as a function of Ganymede’s magnetic latitude and orbital elongation. The investigation of the aurora is a diagnostic tool of the various processes that contribute to Ganymede’s complex magnetic field environment. We find both spatial inhomogeneities as a function of planetary longitude and temporal variation as a function of Ganymede’s position relative to the current sheet in Jupiter’s magnetosphere.