Something “special and unforeseen” is causing a huge aurora across Saturn’s polar cap, NASA scientists report this week in Nature.

“We’ve never seen an aurora like this elsewhere,” says Tom Stallard, lead author of the paper and a researcher at the University of Leicester (press release). “It’s not just a ring of auroras like those we’ve seen at Jupiter or Earth. This aurora covers an enormous area across the pole.”

MSNBC’s Cosmic Log notes:

On Earth and Jupiter, for instance, astronomers are used to seeing auroral arcs or rings of light – which glow when energetic particles stream along a planet’s magnetic field and interact with the atmosphere. The auroras on Earth, also known as the northern or southern lights, are sparked by the solar wind. Jupiter’s main auroral ring is powered by the planet’s own magnetic processes.

Saturn’s main auroral ring, like Earth’s, is caused by the solar wind. But the newly observed infrared displays go all over the place.

“This aurora appears to be unique to Saturn and cannot be explained using our current understanding of Saturn’s magnetosphere,” the authors write in their paper.

Working out how it is triggered by “something special and unforeseen” in interactions between the solar wind and the planet’s magnetosphere and atmosphere will “lead us to physics which uniquely operates in the environment of Saturn,” says fellow author Nick Achilleos, of University College London.

Image: aurora and underlying atmosphere at two wavelengths of infrared / NASA/JPL/University of Arizona