An aurora is a beautiful display of natural lights in the sky, usually seen near the North and South Poles at night. Scientists have long believed that aurorae are created when the solar winds interact with the Earth’s magnetic field — when streams of electrified particles emitted by the Sun are trapped in the magnetic field of the Earth. This is usually the case on other planets as well. But scientists from University of Leicester claim they have discovered that not all aurorae are created by this phenomenon. They say they have found a never-before-seen mechanism creating planetary aurorae at Saturn’s south pole.

What is this mechanism? The scientists say some of Saturn’s aurorae are generated by swirling winds within the planet’s own atmosphere and not just by the interaction between the solar wind and its magnetosphere. This discovery has changed the understanding of planetary aurorae. It also solves one of the mysteries about Saturn — why have we been unable to measure the length of a day on the planet?

NASA launched the Cassini probe in 1997, which reached Saturn in 2004. Since then, it has tried to measure how fast it spins to determine the length of its day. This is done by tracking radio emission ‘pulses’ from Saturn’s atmosphere. Scientists were surprised to find that Saturn’s bulk rotation rate appeared to have changed since the Voyager 2 spacecraft had flown past the planet in 1981.

The scientists have published their findings in American Geophysical Union’s Geophysical Research Letters.

A report by the University of Leicester quoted researcher Nahid Chowdhury as saying that the true rotation rate of a planet cannot vary this quickly, according to their understanding of planetary inner mechanics, and so, something unusual must be happening at Saturn.

They found that a significant proportion of Saturn’s aurorae are generated by the swirling pattern of weather in its atmosphere and are responsible for the planet’s observed variable rate of rotation.

Chowdhury said their study is the first detection of the fundamental driver, situated in the upper atmosphere of the planet, which generates the aurorae.

He added this will likely prompt some reconsideration of how the effects of local atmospheric weather on a planet impact the formation of aurorae.