A stunning light display over Saturn has stumped scientists who say it behaves unlike any other planetary aurora known in our solar system.
The blueish-green glow was found over the ringed planet's north polar region just like Earth's northern lights.
It was discovered by the infrared instruments on NASA's Cassini spacecraft.
The northern polar region of Saturn shows both the aurora and underlying atmosphere, as captured by NASA's Cassini spacecraft
'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.'
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.
A green aurora dances over the night side of the Earth as seen from the International Space Station in 2003. Earth, Jupiter and Saturn all have dazzling auroras
Jupiter's main auroral ring is caused by interactions in Jupiter's magnetic environment and remains constant in size. Saturn's main aurora is caused by the solar wind, and changes size dramatically as the wind varies. However, the newly observed aurora at Saturn doesn't fit into either category.
The new infrared aurora appears in a region hidden from NASA's Hubble Space Telescope. Cassini observed it when the spacecraft flew near Saturn's polar region.
In infrared light, the aurora sometimes fills the region from around 82 degrees north all the way over the pole. This new aurora is also constantly changing, even disappearing within a 45 minute-period.
'There is something special and unforeseen about this planet's magnetosphere and the way it interacts with the solar wind and the planet's atmosphere,' Cassini scientist Nick Achilleos from the University College London said.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency.
