An infrared camera aboard NASA’s Cassini spacecraft discovered an aurora lighting up Saturn’s polar cap. This mysterious new finding is unlike any other known in our solar system.
“We’ve never seen an aurora like this elsewhere,” said Tom Stallard, who works with Cassini data at the University of Leicester. “It’s not just a ring of aurorae like those we’ve seen at Jupiter or Earth. This one covers an enormous area across the pole. Our current ideas on what forms Saturn’s aurorae predict that this region should be empty, so finding such a bright one here is a fantastic surprise.”
Charged particles streaming along a planet’s magnetic field and into its atmosphere create aurorae. On Earth, these charged particles come from the solar wind — a stream of particles that emanates from the Sun.
Jupiter’s main auroral ring is caused by interactions inside Jupiter’s magnetic environment and is constant in size. Saturn’s main aurora, the solar wind causes, changes size dramatically as the wind varies. The newly observed aurora at Saturn, however, doesn’t fit into either category.
“Saturn’s unique auroral features are telling us 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,” said Nick Achilleos, Cassini scientist on the Cassini magnetometer team at the University College in London. “Trying to explain its origin will no doubt lead us to physics which uniquely operate in the environment of Saturn.”
The new infrared aurora appears in a region hidden from NASA’s Hubble Space Telescope, which provided views of Saturn’s ultraviolet aurora. Cassini observed it when the spacecraft flew near Saturn’s polar region. In infrared light, the aurora sometimes fills the region from around 82° north all the way over the pole. This new aurora constantly changes and even disappears within a 45 minute-period.