Auroras are caused by charged particles streaming along the magnetic field lines of a planet into its atmosphere.
Particles from the sun cause Earth's auroras. Many, but not all, of the auroras at Jupiter and Saturn are caused by particles trapped within the magnetic environments of those planets.
'We've never seen an aurora like this elsewhere,' said Tom Stallard, a scientist working with Cassini data at the University of Leicester.
'This aurora covers an enormous area across the pole. Our current ideas on what forms Saturn's aurora predict that this region should be empty, so finding such a bright aurora here is a fantastic surprise.'