The Io, Europa and Ganymede auroral footprints at Jupiter in the ultraviolet: positions and equatorial lead angles

Kavli Affiliate: George Clark

| First 5 Authors: Vincent Hue, Randy Gladstone, Corentin K. Louis, Thomas K. Greathouse, Bertrand Bonfond

| Summary:

Jupiter’s satellite auroral footprints are a consequence of the interaction
between the Jovian magnetic field with co-rotating iogenic plasma and the
Galilean moons. The disturbances created near the moons propagate as Alfv’en
waves along the magnetic field lines. The position of the moons is therefore
"Alfv’enically" connected to their respective auroral footprint. The angular
separation from the instantaneous magnetic footprint can be estimated by the
so-called lead angle. That lead angle varies periodically as a function of
orbital longitude, since the time for the Alfv’en waves to reach the Jovian
ionosphere varies accordingly. Using spectral images of the Main Alfv’en Wing
auroral spots collected by Juno-UVS during the first forty-three orbits, this
work provides the first empirical model of the Io, Europa and Ganymede
equatorial lead angles for the northern and southern hemispheres. Alfv’en
travel times between the three innermost Galilean moons to Jupiter’s northern
and southern hemispheres are estimated from the lead angle measurements. We
also demonstrate the accuracy of the mapping from the Juno magnetic field
reference model (JRM33) at the completion of the prime mission for M-shells
extending to at least 15RJ . Finally, we shows how the added knowledge of the
lead angle can improve the interpretation of the moon-induced decametric

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