Aurora in the air
Ganymede, the Jovian moon, has two planet-like features which were discovered last year: a magnetic field and the trace of an atmosphere. New data from the Hubble Space Telescope reveals that it might have a third planetary feature, an aurora at the poles. Doyle Hall and his colleagues of the Johns Hopkins University in the US have detected a very faint aurora.
The basic mechanism is thought to be the same as for planetary auroras: the magnetic field channels high-energy particles into polar regions where they collide with gas molecules to give off (in this case) ultraviolet radiation.