The moon-induced auroral emissions at Jupiter:a natural probe of the atmosphere and magnetosphere

At Jupiter, the fast planetary rotation, the strong magnetic field and the presence of a relatively high density plasma create a powerful electromagnetic environment. Jupiter’s auroras are one evidence of the strong magnetospheric activity around the planet. The interaction between the four major moons of Jupiter - Io, Europa, Ganymede and Callisto - and the Jovian magnetosphere produces satellite-induced auroral emissions, called footprints. These are caused by the flow of magnetospheric plasma past the moons, which triggers a local perturbation that generates mainly Alfvén waves propagating down to the planetary atmosphere. Here, the Alfvén waves accelerate electrons into the ionosphere, where auroral emissions are generated. The morphology of the footprints depends on the shape of the wave-fronts of the Alfvén waves that bounce in the magnetospheric cavity. The propagation of these waves is mainly affected by the magnetic field and plasma density, therefore, the footprint implicitly contains information on those quantities. 
Since 2016, the Juno mission has been providing high-quality observations of the Io footprint in the infrared (IR) and ultraviolet (UV) bands. We propose an overview of the IR and UV observations of the footprints from Juno, with a particular focus on Io, to highlight how the observations of the footprints can fulfill multiple purposes, such as monitoring plasma conditions in the magnetosphere, and investigating the vertical structure of the ionosphere. We show the comprehensive dataset of the observations, which is compared to previous observations from Hubble and to magnetic field models. The agreement with the magnetic field model based on the Juno magnetometer is overall very good, with the major deviations in the northern anomaly region. The position of the footprints can be used to constrain the plasma conditions at the orbit of the moons, therefore we use the IR and UV observations of the Io footprint to determine the density and temperature of the Io Plasma Torus around Jupiter between 2016 and 2022. To support this survey, the radio occultations performed by the radio tracking systems have been included, as they wrap information on the electron content of the Io Plasma Torus. This analysis suggests that the Io Plasma Torus can exhibit large variations (factor ~2-3) in density and temperature over a couple of months. We are currently investigating the UV vertical profile of the Io footprint by using limb observations, which allow to constrain the energy distribution of the precipitating particles and the energy deposition, and the location of the methane homopause, which absorbs part of the UV emission and destroy the H₃⁺ responsible for the IR emission.