Abstract :
[en] The Hubble Space Telescope's high resolution observations of the Jovian aurorae in the UV domain have provided us with a wealth of new information in the recent years. Not only do we have now access to details down to a couple hundreds kilometers, but we can also analyze changes on timescales of tens of seconds. These images and spectra have taught us that the aurorae are made of many different features, each of them associated with a different process in the Jovian magnetosphere. This magnetosphere significantly differs from the Earth's one, being dominated by the rapid rotation of Jupiter and the plasma originating from Io's volcanism.
The satellite footprints are the auroral signature of the electro-magnetic interaction between the Galilean moons and the magnetospheric plasma rotating around Jupiter. In the case of Io, Europa and Ganymede, this signature takes the form of a chain of spots followed by an elongated tail of emission. The tentative identification of a Callisto footprint will also be discussed. Poleward of Io's footprint, patches of emission of various sizes have been associated with injections of hot coming from the outer magnetosphere into the middle magnetosphere. These spots ares thus important markers of the plasma circulation in the Jovian magetnosphere. In the same auroral region, more diffuse emissions are associated with pitch angle scattering in the magnetospheric area where dipolar magnetic field lines become elongated.
The most striking feature of the Jovian aurorae is the main emission. This structure sometimes appears as a continuous auroral oval, but it can also display much more complex patterns, especially on the dusk side. Moreover, the brightness strongly changes with local time, as a response to the variability of the corotation enforcement currents and the partial ring currents in the middle magnetosphere.
Directly poleward of the main emission, patches regularly appear on the night and dawn sides, in a region generally devoid of any emissions (the polar dark region). Such patches are thought to be a signature of the reconnection process that allows the release of the plasma coming from Io into the magnetotail. The dusk side of the area enclosed in the main emission, called the active region, is the locus of intense and transient (sometimes, even quasi-periodic) flares as well as more stable arcs and diffuse patches. Poleward of this area, stable filaments can sometimes be seen along the noon to midnight axis. Finally, the polar-most region, tentatively associated with open field lines, display rapidly fluctuating patches of emissions. All these polar emissions are very poorly understood and will thus be the subject of fascinating investigations from the Juno spacecraft, arriving around Jupiter on July 4th.