Saturn A display of bright, flickering lights has mystified scientists because it behaves unlike any other known aurora.

The aurora, which like the northern lights on Earth is over one of the poles, was detected by an infra-red camera carried by Nasas Cassini spacecraft.

Tom Stallard, of the University of Leicester, said: Its not just a ring of aurorae like those weve seen at Jupiter or Earth. This one covers an enormous area across the pole.

Our current ideas on what forms Saturns aurorae predict that this region should be empty, so finding such a bright one here is a fantastic surprise. The image shown on the left is a composite displaying the aurora, illustrated in blue, the planets hot interior, rendered in red, and clouds, which appear as black silhouettes.

Particles crashing into the planets atmosphere cause the glow, which has a wavelength of 4 microns, six times that of light visible to the human eye. The aurora image was actually taken two years ago, from a distance of 1,061,000 kilometres (659,000 miles). The image of the clouds was taken in June this year, from 602,000 kilometres.

The mission is a cooperative project of Nasa, the European Space Agency and the Italian Space Agency.