'Decagon' at Saturn’s South Pole? After the long-lived 'hexagon' at its north pole, astronomers spot a mysterious 10-sided atmospheric wave in the planet’s southern hemisphere - Here’s what we know so far

Saturn has spent decades surprising scientists with its strange weather, but its latest atmospheric mystery may be one of its most unusual yet. Astronomers have discovered a giant, evolving 10-sided atmospheric wave around Saturn’s south pole, giving the ringed planet a striking geometric feature on the opposite side of its famous northern hexagon. The discovery comes from observations by NASA’s Hubble Space Telescope, combined with years of ground-based observations. Researchers say the newly identified 'decagon' appears to be developing within one of Saturn’s powerful jet streams and extends through multiple atmospheric layers. Unlike the northern hexagon, which has remained remarkably stable for more than 40 years, the southern decagon appears to be strengthening and evolving. Scientists are now watching closely to understand what created it and whether it will survive.


HUBBLE CAPTURES SATURN’S SOUTHERN MYSTERY


The discovery emerged from several years of observations. Ground-based observers first noticed a subtle undulating band near Saturn’s south pole in 2024, while Hubble observations later confirmed that the developing pattern was already present in data from 2023 with stronger evidence appearing in 2025. The research was led by Agustín Sánchez-Lavega, a planetary scientist at the University of the Basque Country, Spain. NASA’s Amy Simon, principal investigator of Hubble’s Outer Planet Atmospheres Legacy (OPAL) program, is a co-author, along with Michael Wong of the University of California, Berkeley and other colleauges. The findings were published in Science Advances. The OPAL program has been especially important because it repeatedly photographs the outer planets. Instead of providing only one snapshot, these observations allow researchers to follow atmospheric features as they appear, strengthen or disappear.

"Given Saturn’s symmetry in its north-south jet stream system, we have been searching for a counterpart to Saturn’s northern hexagon on the south pole in Hubble images since 1990," Sánchez-Lavega stated in a NASA press statement. "Images from NASA’s Cassini spacecraft, which orbited Saturn between 2004 and 2017, showed no inkling of a long-lived formation, either. The Hubble data confirmed the feature’s presence back to 2023."

A SOUTHERN COUSIN TO SATURN’S FAMOUS HEXAGON?

Saturn’s north pole has hosted one of the solar system’s most recognizable atmospheric structures: a giant hexagonal jet-stream pattern first identified in Voyager-era observations. Scientists have searched for a comparable southern feature for decades. The new decagon is intriguing because it occupies a similar polar environment, but researchers stress that it is not simply a southern analogue of the hexagon. The northern hexagon has remained remarkably stable for more than four decades. The southern decagon, by contrast, appears to be strengthening and evolving. NASA says this gives scientists a rare opportunity to watch a giant atmospheric pattern develop rather than simply study one that has already reached a stable state. The newly observed structure also sits inside one of Saturn’s powerful jet streams. Observations at different wavelengths suggest that the wave extends through multiple levels of the atmosphere, meaning it is more than a pattern confined to a single visible cloud layer.

WHAT COULD HAVE CREATED THE DECAGON?

That is the biggest unanswered question. Sánchez-Lavega and his colleagues are investigating how Saturn’s atmospheric circulation can produce such a regular polygonal pattern. The researchers also want to determine whether the decagon will eventually settle into a stable configuration or continue changing. The timing makes the discovery particularly valuable. Saturn’s seasonal cycle gradually brought its southern hemisphere back into view after the region had become difficult to observe from Earth. Hubble’s long-term observations then allowed scientists to trace the feature backward to at least 2023. Future observations could provide even more clues. Researchers plan to continue using Hubble, study observations from the James Webb Space Telescope, and compare the observations with computer models of Saturn’s atmosphere.

WHY SATURN’S DECAGON MATTERS

The discovery is about much more than an unusual shape. Polygonal atmospheric patterns offer scientists a natural laboratory for studying jet streams, atmospheric waves and circulation on giant planets. The contrast between Saturn’s long-lived northern hexagon and its apparently younger southern decagon could be especially revealing. One has remained stable for decades, while the other is still developing.

For now, scientists do not know whether Saturn’s new 10-sided feature will become a permanent landmark or eventually fade away. But that uncertainty is exactly what makes the discovery so exciting. As Amy Simon noted, researchers have never seen anything quite like this in Saturn’s southern hemisphere. Continued monitoring could show scientists how a planetary atmosphere creates - and perhaps destroys - one of nature’s most striking geometric patterns.