The length of the Io footprint: Spectral characterization using Juno-UVS

The vast Jovian magnetosphere is filled with plasma originating from Io's volcanic activity in the inner magnetosphere. This plasma is structured as a sheet in near-corotation with Jupiter's magnetic field and confined to the centrifugal equator. The Galilean moons act as physical obstacles to this plasma flow, generating Alfvén wings. The propagation and reflection of Alfvén waves between Jupiter's northern and southern polar ionospheres create several auroral spots, whose brightness and morphology are controlled by the moon's position within the plasma sheet. These initial Alfvén waves progressively lose energy as they undergo multiple partial reflections between Jovian hemispheres, characterized by the brightness decrease of the auroral footprint tail downstream of the main spot in ultraviolet and infrared spectra. Previous observing campaigns using the Hubble Space Telescope have characterized this brightness decrease, measuring an ultraviolet e-folding distance of 21,000 km, correponding to about 40˚ of longitude (Bonfond, et al. 2009, The Io UV footprint: Location, inter-spot distances and tail vertical extent, J. Geophys. Res., 114, A07224, doi:10.1029/2009JA014312.). Juno's unique vantage point in the Jovian system now allows for measurements of the entire Io footprint structure at almost every perijoves, using the Juno-UVS instrument. We extend previous work characterizing the Io footprint by analyzing the Juno-UVS dataset collected during the Juno prime mission.