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

The interaction between the four major moons of Jupiter - Io, Europa, Ganymede and Callisto - and the Jovian magnetic field generates satellite-induced auroral emissions, called footprints. These are caused by electrons precipitating into the ionosphere by wave-particle interaction with the Alfvén waves that are generated by the plasma flow impinging onto the moon. The position and inter-spot distance of the footprints mirror the shape of the wave-fronts of these Alfvén waves, whose propagation is mainly affected by the magnetic field and plasma density. Consequently, the footprint implicitly contains information on those quantities.

The Juno mission has been providing high-quality observations of the Io footprint in the infrared (IR) and ultraviolet (UV) bands since 2016. We propose an overview of the Io footprints from Juno’s perspective, with the goal of showing how the footprint can be used 1) to monitor the plasma conditions near the moon, and 2) to investigate the structure of the Jovian ionosphere. For the first aspects, we use the IR and UV observations of the Io footprint to constrain the density and temperature of the Io Plasma Torus around Jupiter from 2016 to 2022. To support this survey, we also include the radio occultations performed by the radio tracking systems, as they are sensitive to the electron content of the Io Plasma Torus. For the second goal, we are investigating the UV vertical profile of the Io footprint, which combines information about the hydrocarbon distribution in the upper atmosphere with the energy distribution of the precipitating particles. We will show how to determine the presence of methane, ethane and acetylene using the UV spectrum measured by Juno, and how to derive the energy distribution of the precipitating electrons from the vertical profile of the emission.