Saturn, apparently, has been hiding its talents.
For decades, humanity has puzzled over the gas giant’s enormous hexagon swirling around its north pole – a six-sided atmospheric structure unlike anything else known in the Solar System.
Now, it seems, that bizarre feature is not an isolated incident – and Saturn may have a propensity for polygons, rather than a passing whim.
Lurking around the planet’s south pole, astronomers led by Agustín Sánchez-Lavega of the University of the Basque Country in Spain have spotted another giant polygon – and this one has ten sides.
“This discovery suggests that the hexagon is not as extraordinary as previously thought and that, in fact, the conditions in Saturn’s atmosphere are such that polygonal waves can form in both hemispheres surrounding the polar regions,” Sánchez-Lavega told ScienceAlert.
Saturn’s most prominent and well-known feature is its magnificent system of icy rings, but the hexagon at its north pole would have to be a pretty close second.
It was first discovered in images from the Voyager probes in 1980 and 1981: a vast, six-sided atmospheric wave swirling around the pole at about 78.5 degrees latitude.
In the intervening decades, both the Hubble Space Telescope and the Cassini-Huygens Saturn probe also captured the strange feature, suggesting that it has remained stable for at least 44 years.
It’s a weather phenomenon, but why it has such an almost perfect polygonal shape remains a mystery. And although scientists also thought Saturn’s southern subpolar jets might produce a similar feature, none revealed itself across multiple searches.
Then, in 2024, polygon lightning struck for the second time.
In images from amateur astronomers, a dark, undulating line was visible around the planet’s south pole.
Work in 2025 confirmed it. While creating polar projections from images of Saturn taken by astronomers Trevor Barry of Broken Hill Observatory in Australia and Jean-Paul Oger of the French Astronomy Association, the team finally saw it: Ten sides, forming an unmistakable polygon around the pole.
High-quality images from the Hubble Space Telescope confirmed it and allowed the team to trace it back to 2023.
“The discovery of the wave really did come as a surprise, as neither earlier images of Saturn taken by the Hubble Space Telescope nor those captured by the Cassini spacecraft whilst orbiting the planet between 2004 and 2017 had shown it,” Sánchez-Lavega said.
Centered around 60 degrees south, the decagon appears to be a vast atmospheric wave riding on one of Saturn’s powerful eastward jet streams. The jet itself races around the planet at roughly 420 kilometers (260 miles) per hour, while the decagon moves at a comparatively leisurely place of around 10 kilometers per hour.
Like the hexagon, the decagon doesn’t appear to be just a pattern sitting across the visible cloud tops. Observations at different wavelengths revealed traces of its shape at different altitudes and latitudes, suggesting a vast, vertically layered structure embedded in Saturn’s atmosphere.
Fundamentally, it is the same kind of phenomenon as the hexagon, but – difference in side count notwithstanding – the two polygons are not mirror images of each other.
“In addition to the difference in the number of sides,” Sánchez-Lavega explained, “the decagon is situated at a less polar latitude than the hexagon in the southern hemisphere, and is perhaps not as robust, as we have seen that it has formed.”
There are so many questions about these differences. Why did the decagon only form a few years ago, compared to decades of stability for the hexagon? Why are their latitudinal positions different?
And why does the southern polygon have ten sides, compared to the north’s nature-preferred six?
“It may be linked to the difference in latitude, to the background wind structure, or perhaps even to the presence of a high-pressure vortex at nearby latitudes that could be forcing the formation of the wave,” Sánchez-Lavega told ScienceAlert.
There’s even a plausible suspect.
Just north of the decagon is a roughly 4,000-kilometer-wide anticyclone – a high-pressure vortex the researchers call a Red Spot – smaller, temporary analogs of Jupiter’s famous storm. Intriguingly, the decagon appears most pronounced near the vortex and least distinct on the opposite side of the planet.
The researchers conducted simulations to determine whether this storm – or some other disturbance – could have played a role in the formation of the decagon.
None of their scenarios, however, was able to reproduce the observed decagon exactly.
And, of course, there’s this little snag.
“The hypothesis that a nearby anticyclone at that latitude is driving the oscillation is an attractive one,” Sánchez-Lavega said. “The same thing happened with the hexagon when it was discovered in 1980, but then the nearby vortex disappeared, and the hexagon remained.”
So for now, the answer is tantalizingly out of reach. Currently, the decagon is still there – observing how it changes over the coming months and years could reveal much more about how it formed.
Saturn is tilted on its axis as it orbits the Sun every 29.5 years, giving the planet long seasons lasting about 7.5 years each. Its southern hemisphere is now moving through spring towards summer, tilting increasingly towards the Sun.
Related: Amazing New Photos of Saturn’s Moons Have to Be Seen to Be Believed
The increase in solar radiation hitting the southern hemisphere – and the decagon – could cause some interesting changes. And as the south pole tilts further into view, astronomers will have an increasingly good vantage point from which to watch them unfold.
“We need to understand how the decagon evolves – in other words, whether in the coming years it will become unstable and break up, or, conversely, become more stable and robust as solar radiation increases,” Sánchez-Lavega said.
Saturn’s hexagon has endured for at least 44 years; we only learned of its existence well after it was established.
With the decagon, scientists now have a front-row seat to how Saturn builds its polygons in real time – and whatever happens, it’s going to be one heck of a show.
The research has been published in Science Advances.
This article was fact-checked by Fiona MacDonald and edited by Fiona MacDonald. While we pride ourselves on our process, we are only human. If you spot a mistake, please let us know.
