An international group of astronomers discovered a previously unknown mechanism behind the massive aurorae on the poles of Saturn, a press statement reveals.
The researchers found that, unlike any other planet observed to date, Saturn generates aurorae by swirling winds within its own atmosphere, and not only from the magnetosphere surrounding the planet — as is the case on Earth.
The new discovery shows that Saturn has a truly unique aurora, and it is the only one known to truly live up to the name "Aurora Borealis", which was designated before humans knew the precise science behind the stunning natural light show. It also answers one of the questions raised by NASA's Saturn-orbiting Cassini probe mission which launched in 1997 and reached the planet in 2004. Namely, why is it so hard to measure the length of a day on Saturn?
"It's absolutely thrilling to be able to provide an answer to one of the longest-standing questions in our field. This is likely to initiate some rethinking about how local atmospheric weather effects on a planet impact the creation of aurorae, not just in our own Solar System but farther afield too," University of Leicester Ph.D. researcher Nahid Chowdhury, co-author of a new paper on the subject published Geophysical Research Letters, said.
Saturn has "a true Aurora Borealis"
When NASA's Cassini probe first arrived at Saturn, it tracked radio emission 'pulses' from the planet's atmosphere in an attempt to try to measure its bulk rotation rate. Doing this would allow scientists to determine the length of the ringed planet's days. To the surprise of NASA's ground team, the rate appeared to have changed since NASA's Voyager 2, the previous spacecraft to have flown past Saturn, took readings in 1981. This impeded researchers from calculating the exact length of a day on the sixth planet away from the Sun.
Thankfully, scientists did develop a new method that allowed them to determine the length of a Saturn day in 2019. They used gravity-induced perturbations in Saturn's ring system to measure the days as lasting 10 hours, 33 minutes, and 38 seconds.
Now, the new study shows why it was such a challenge to measure Saturn's days, and it's closely linked to the mechanism behind the unique type of aurorae found on the planet. Dr. Tom Stallard, Associate Professor in Planetary Astronomy at the University of Leicester said, "we now know that aurorae on Earth are powered by interactions with the stream of charged particles driven from the Sun. But I love that the name Aurora Borealis originates from the 'the Dawn of the Northern Wind'. These observations have revealed that Saturn has a true Aurora Borealis — the first-ever aurora driven by the winds in the atmosphere of a planet."
In their new study, the international team of researchers mapped the varying flows of Saturn's ionosphere for a month in 2017. When comparing this data to the known pulse of Saturn's radio aurorae, they found that the planet's aurorae are generated by the swirling weather patterns in its atmosphere. These, they also observed, are responsible for the discrepancies in the observation of Saturn's variable rate of rotation.