Northumbria University team solves Saturn rotation mystery

A research team led by scientists at Northumbria University has revealed the cause of Saturn’s changing spin rate, a question that has baffled scientists for decades.

By using the James Webb Space Telescope (JWST) to observe the planet’s northern lights in unprecedented detail, the team discovered a self-sustaining cycle of heat and electrically charged particles powered by the aurora itself.

Professor Tom Stallard, lead researcher and professor of planetary astronomy at Northumbria University (Image: Supplied)

Saturn has long puzzled astronomers.

In 2004, data from NASA’s Cassini spacecraft suggested that the planet’s rotation rate was shifting over time—something not thought possible.

Professor Tom Stallard, lead researcher and professor of planetary astronomy at Northumbria University, said: “What we are seeing is essentially a planetary heat pump.

“Saturn’s aurora heats its atmosphere, the atmosphere drives winds, the winds produce currents that power the aurora, and so it goes on.

“The system feeds itself.”

Research in 2021 led by Professor Stallard identified upper atmospheric winds as the source.

These winds, not actual rotation, were producing electrical currents that distorted the auroral signals and gave the illusion of a variable spin rate.

The team’s latest study, published in the Journal of Geophysical Research: Space Physics, used JWST to observe Saturn’s northern auroral region over a full Saturnian day.

By examining the infrared signature of the trihydrogen cation, a molecule in Saturn’s upper atmosphere that acts as a thermometer, the team mapped temperature and particle density at higher resolution than ever before.

These patterns matched predictions from computer models—but only if the primary source of heat was located at the site of the auroral emissions.

This confirms that Saturn’s aurora directly heats the atmosphere, powering winds that produce the currents responsible for the aurora in a continuous feedback loop.

Professor Stallard said: “For decades, we knew something strange was happening with Saturn’s apparent rotation rate, but we could not explain it.

We then showed it was being driven by atmospheric winds, but we still did not know why those winds existed.

“These new observations, made possible by JWST, finally give us the evidence we needed to close that loop.”

The findings have broader implications, suggesting a two-way relationship between Saturn’s atmosphere and its magnetosphere—the enormous region of space shaped by the planet’s magnetic field.

Professor Stallard said: “This result changes how we think about planetary atmospheres more generally.

If a planet’s atmospheric conditions can drive currents out into the surrounding space environment, then understanding what is happening in the stratospheres of other worlds may reveal interactions we have not yet even imagined.”

The study was a collaboration between researchers in the UK and US, including teams from Boston University, the University of Leicester, and Aberystwyth University.