The morphology of Io’s ultraviolet aurora

The Jupiter moon Io is the most volcanically active world in the solar system and the main source of material for Jupiter’s magnetosphere. It is unique in detailed characteristics like its interior layering, tidal forces at play, variable surface features, the dynamics of the short-lived atmosphere and the electrodynamic interaction with the strong magnetic field of Jupiter. However, the processes that drive the atmospheric escape of neutrals (mostly S and O) and the formation of neutral clouds within the plasma torus are not fully understood yet. To address these open questions, data from the Space Telescope Imaging Spectograph (STIS) instrument of the Hubble Space Telescope (HST) are analyzed regarding to temporal variations in the auroral emissions of different species present in Io’s atmosphere. Io’s aurora consists of three different patterns. The most prominent are the equatorial spots, caused by electron impacts from flux tubes that convect over Io. The spot’s position varies dependent on Io’s position relative to the Jovian magnetic field. Secondly, Io emits UV radiation from its limbs as seen from HST. The brightness of this limb glow is proportional to the electron density of the surrounding plasma. By comparing the limb glow’s brightness on Io’s Northern and Southern hemisphere, it is possible to extract an electron density distribution for the plasma torus. Lastly, escaping and not-escaping particles within Io’s extended exosphere radiate and contribute to the emissions. The observation of the exosphere can provide information about the formation of neutral clouds within the plasma torus.