Aurora in the air

Published: Saturday 30 November 1996

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.

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