Scientists solve the mystery behind the cause of Saturn’s extraordinary aurora

Saturn is different from all other planets because its aurorae are generated by winds in its atmosphere as well as its magnetosphere

(NASA, Cassini, VIMS Team, University of Arizona, University of Leicester, JPL, ASI)

Scientists have discovered a never-before-seen mechanism that explains the huge planetary aurorae on the planet Saturn.

Saturn has been found to be different from all other planets, including Earth, because its aurorae are generated by winds within its own atmosphere as well as from its magnetosphere – something that does not happen anywhere else in the known universe.

Researchers believe the system is driven by energy from Saturn’s thermosphere, while wind speeds in the ionosphere can reach up to three kilometres per second.

These winds are powered by charged particles from the Sun or volcanic material erupted from a moon orbiting the planet.

This new discovery answers the question raised by Nasa’s Cassini probe which reached the planet in 2004: why is it so difficult to measure the length of a day on Saturn?

Cassini tried to answer this using the bulk rotation rate of the planet by tracking emission ‘pulses’ from the atmosphere, but it appeared that the speed of the planet had changed from the last measurement taken by Voyager 2 in 1981. Eventually, a new method was used to determine the rate was 10 hours, 33 minutes and 38 seconds.

“Saturn’s internal rotation rate has to be constant, but for decades researchers have shown that numerous periodic properties related to the planet – the very measurements we’ve used at other planets to understand the internal rotation rate, such as the radio emission – tend to change with time. What’s more, there are also independent periodic features seen in the northern and southern hemispheres which themselves vary over the course of a season on the planet”, Leicester researcher Nahid Chowdhury said in a statement.

“Our understanding of the physics of planetary interiors tells us the true rotation rate of the planet can’t change this quickly, so something unique and strange must be happening at Saturn … This study represents the first detection of the fundamental driver, situated in the upper atmosphere of the planet, which goes on to generate both the observed planetary periodicities and aurorae.”

Scientists had long-debated the root cause of these lights, hypothesising that it could be caused by the volcanic moon Enceladus or interactions with the thick atmosphere of the moon Titan.

“Our study, by conclusively determining the origin of the mysterious variability in radio pulses, eliminates much of the confusion into Saturn’s bulk rotation rate and the length of the day on Saturn,” Dr Kevin Baines, co-author of the study and a member of the Cassini Science Team, said.

The research was published in Geophysical Research Letters.