Astronomers just spotted an enormous, 10-sided shape surrounding Saturn‘s southern skies.
They call it a decagon because it has 10 corners and 10 long sides. It rings the planet’s southern mid-latitudes, where a powerful jet stream races around the globe.
From Earth, we don’t literally look up at Saturn’s underbelly. Instead, Saturn tilts on its axis, so its poles lean toward or away from us in space over its long seasons. For more than a decade, the south stayed tipped away, and even our best telescopes could not see those latitudes clearly.
But when Saturn’s tilt swung the south pole back toward Earth, NASA‘s Hubble Space Telescope and large ground‑based observatories finally gained a clear view from 2023 to 2025.
That timing explains why the decagon appears only now and why scientists are so interested. Researchers say it gives them a chance to watch how a giant planet can sculpt its winds into sharp, angular shapes in real time.
So what is this thing, really? The decagon is not a ring of solid clouds in Saturn’s sky. It’s a giant atmospheric wave — a repeating bend in the winds that runs all the way around the planet.
Waves in air behave similar to waves in an ocean. Water doesn’t pick up and slide across the sea in one big piece; instead, it rises and falls in place as the wave shape passes by.
Credit: NASA / ESA / Agustin Sánchez-Lavega / Amy Simon / Michael Wong / Alyssa Pagan
Details about the new phenomenon were published in Science Advances.
If aliens on Saturn were to point the same telescopes at Earth, they would not see such geometric shapes in our clouds. Here, high‑altitude winds in the jet stream sometimes wobble north and south. Those bends help steer cold snaps, heat domes, and storm tracks. From space, they look messy and lumpy because continents, mountains, and coastlines keep chopping them up.
But Saturn has no continents or mountains — only deep layers of gas. That clean racetrack lets waves in the jet fall into regular patterns.
In the southern jet that hosts the decagon, the wind wiggles slightly toward the pole and slightly toward the equator as it flows. Where the wave bends one way, clouds pile up or brighten. Where it bends the other way, clouds thin out or darken. Up close, nothing actually has knife‑sharp edges, even on that alien world. But the repeated pattern tricks our eyes into seeing lines and corners.
“The most intriguing part to me is that this seems to have just formed recently,” said Amy Simon, a co-author of the study based at NASA’s Goddard Space Flight Center, in a statement. “The question is, why did it suddenly form now when we haven’t seen one before?”
Credit: NASA / ESA / Agustin Sánchez-Lavega / Amy Simon / Michael Wong / Alyssa Pagan
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The decagon is enormous. Each side spans on the order of 10,000 miles. A jet stream under it tears along at about 260 mph, while its corners slowly shift back and forth over roughly month‑long cycles.
The structure also seems to evolve. Hubble images from 2023 show only weak hints of corners. By 2024 and 2025, all 10 points appear, though some look brighter and sharper.
A nearby storm adds another wrinkle. Just north of the decagon, astronomers track a red spot a few thousand miles wide — not to be confused with the solar system’s most famous Great Read Spot on Jupiter. In some colors, it looks bright, which means its clouds reach higher than the surroundings. In ultraviolet light, it looks dark.
The strongest corners of the decagon gather near this storm. That proximity hints that the storm and the wave share energy in the same jet, and the red spot may help trigger or influence the shape.
To test ideas, scientists built a computer simulation of Saturn’s weather layer at those latitudes. They set the model’s winds to match the jet, then poked and prodded it in different ways: with a line of small bumps, with a storm like the red spot, and with a neat 10-wave pattern to start.
Credit: NASA / JPL-Caltech /Space Science Institute
Though the details didn’t match the real decagon, the model showed that strong, curved jets can create polygon‑like waves when something nudges them.
Only after they pinned down the southern decagon did researchers compare it to Saturn’s north‑pole hexagon (Yes, there’s another geometric wave pattern up top). The hexagon, with its six sides, has held its shape since the Voyager flybys in the early 1980s. It stands almost fixed relative to Saturn’s rotation and has fairly even sides and corners.
The southern decagon, on the other hand, looks far less stable and only showed up a few years ago. Its corners shift in strength and position, and parts of the pattern look much weaker than others. That difference tells scientists the southern wave may be more ephemeral.
“Images from NASA’s Cassini spacecraft, which orbited Saturn between 2004 and 2017, showed no inkling of a long-lived formation, either,” said Agustín Sánchez-Lavega, lead author of the study.
The new decagon is especially valuable to scientists because it connects to a bigger puzzle across the solar system. On Jupiter, the poles host clusters of cyclones that arrange themselves into ring‑like, sometimes-polygonal patterns. By tracking Saturn’s 10-sided wave through changing seasons and shifting sunlight, scientists hope to learn why some giant‑planet jets settle into tidy structures and others break into tangled storms instead.
