Io, Europa, and Ganymede act as an obstacle to the corotating plasma in the Jovian magnetosphere. Through the electrodynamic interaction at the moons (e.g., Kivelson et al., 2004), Alfvén waves are launched and propagate along the magnetic field. Auroral electrons are accelerated toward/away from Jupiter's atmosphere by the Alfvén waves and ultimately induce multiple satellite auroral footprints and a diffuse auroral tail in Jupiter's atmosphere (e.g., Clarke et al., 2002; Bonfond et al., 2008).

The Alfvén velocity depends on the local magnetic field magnitude and the local plasma mass density. The position of satellite auroral footprints is detemined by the Alfvén wave propagation time. The angular separation between the satellite body and the auroral footprint is called the lead angle. The footprint lead angle has been proven to be useful to investigate temporal variations of plasma parameters in the Io plasma torus (Moirano et al., 2023) and the plasma disc at Europa's orbit (Satoh et al., 2024). Both studies traced the Alfvén waves from the moon to the MAW spot in the plasma sheet with various plasma parameters and estimated the lead angle to find the best fit parameters. Estimation of the plasma parameters at the orbits of the icy moons is important because the magnetospheric plasma controls source and loss of neutral atmospheres in the icy moons.

Now, using the same fitting procedure as Satoh et al. (2024), we’re trying to derive the three ion parameters (atomic mass, number density, and temperature) at the orbits of Io, Europa, and Ganymede, from the footprint lead angle measured by Juno-UVS. In addition to the MAWs, we also use the lead angle of the Transhemispheric Electron Beam (TEB) spot (Bonfond et al., 2008). The TEB spot is generated by the electrons accelerated away from Jupiter in the other hemisphere. Hence, the TEB spot in one hemisphere is strongly associated with the other hemisphere's MAW spot. Using the TEB spot, we can trace the Alfvén waves that have different propagation paths than the ones corresponding to the MAW spot observed in the same hemisphere at the same time, which is expected to add another constraint for the estimation of ion parameters.