Nestled in the outer reaches of the solar system at a distance of almost one billion miles from the sun, Saturn should be cold and dim. And for the most part, it is—except for its surprisingly toasty upper atmosphere, which seems to simmer in the range of about 125 to 325 degrees Celsius (257 to 617 degrees Fahrenheit).
The source of these sweltering temperatures—first detected by NASA’s two Voyager spacecrafts, which zoomed by the gas giant in the 1980s—have long baffled planetary scientists. Now, nearly four decades later, researchers have used new evidence to home in on a probable culprit: the auroras sparking across Saturn’s north and south poles, according to a study published this week in Nature Astronomy.
As Passant Rabie reports for Inverse, the findings come courtesy of NASA’s Cassini spacecraft, which ended its two-decade sojourn through space by plunging down into Saturn’s atmosphere in 2017. In the years before the probe made its final, dramatic descent, it collected troves of data on Saturn’s atmosphere, magnetic field and rings, allowing researchers to map the planet’s characteristics from afar.
Much of data allowed researchers to build on the measurements the Voyager probes had taken, more finely charting out where the planet’s temperatures dipped and soared. These detailed new maps showed that Saturn’s atmospheric temperatures were highest near its poles, at latitudes of roughly 60°N and 60°S—peaks that previous models had failed to predict, study author Zarah Brown, a researcher at the University of Arizona’s Lunar and Planetary Laboratory, tells Inverse.
But these spikes in heat weren’t completely arbitrary because they happened to overlap with known locations of Saturn’s auroras, the gas giant’s equivalents of northern lights on Earth.
According to a statement, auroras—whether here on Earth or elsewhere—occur when charged particles from the sun slam into a planet’s magnetic field. (But don’t expect light shows on Saturn, where auroras glow mainly in ultraviolet wavelengths invisible to the naked eye.) This energetic interaction generates electric currents that then shudder through the planet’s upper atmosphere, infusing aurora-packed regions with heat.
As Lisa Grossman reports for Science News, a similar process happens on Earth—and may be a fixture of other distant planets like Jupiter, Uranus and Neptune, which were also observed to host bizarrely hot upper atmospheres.
“No other giant planet has been studied in this kind of detail,” Brown tells Inverse. “This is really a great starting point.”
As such, the study marks “a big step in our understanding” of how planets’ upper atmospheres can heat up in the absence of copious sunlight, planetary scientist Ron Vervack of Johns Hopkins University’s Applied Physics Laboratory, who wasn’t involved in the study, tells Science News. But as humans continue to explore the rest of the solar system, the story could still shift. “The real test of whether they’re right,” Vervack says, “will be when you go out to Uranus or Neptune.”