Saturn has a decagon-shaped pattern at its south pole
Key takeaways
- Hubble tracking published on 3 September confirms a ten-sided jet pattern circling Saturn's south pole
- It is the first large regular-sided wave recorded in Saturn's southern hemisphere; the north has carried a hexagon since 1981
- Cassini saw nothing there before its mission ended in 2017, and Hubble archive images show it by 2023
- Both Hubble and JWST have follow-up observations planned
Saturn has had a hexagon at its north pole for as long as we have been able to look at it properly. As of this week it has a decagon at its south pole, and the strange part is that nobody saw it arrive.
NASA published Hubble tracking on 3 September confirming a giant, evolving ten-sided atmospheric wave encircling Saturn's south pole. It is the first large regular-sided jet pattern ever recorded in the planet's southern hemisphere.
What is the Saturn decagon at the south pole?
It is a jet stream forced into a standing wave. A jet stream is a fast river of wind, and this one circles the pole. It develops a fixed number of bends, and because the atmosphere beneath it is deep and largely frictionless, those bends hold their shape for years instead of smearing out.
The northern hexagon has kept six sides since Voyager photographed it in 1981. It is enormous, and the jet tracing its edges runs at around 320 km/h (200 mph), according to NASA Cassini imagery reported by Space.com.
Ten sides rather than six is a difference in wind speed and latitude, not in physics. The number of bends depends on how fast the jet runs relative to the rotation of the planet, which is how the two poles can carry different shapes at the same time.
How can wind make a straight-sided shape?
The edges are not solid walls. They are the path of a meandering jet, and the "corners" are the points where the wave bends. Laboratory experiments with a rotating tank of fluid have produced similar polygons, which is part of why researchers trust the basic explanation.
On Earth the same idea appears in the meanders of the jet stream that steers weather across the Atlantic. The difference on Saturn is scale and persistence. There are no continents or oceans to disrupt the flow, so the wave can circle the pole for years without breaking up.
How does it compare with the northern hexagon?
| Feature | North pole hexagon | South pole decagon |
|---|---|---|
| Number of sides | Six | Ten |
| First recorded | Voyager, 1981 | Hubble archive, 2023 |
| Age | Present for four decades | Formed between 2017 and 2023 |
| Confirmed by | Voyager and Cassini imaging | NASA Hubble tracking, 3 September |
| Status | Long-lived and stable | Newly formed, stability unknown |
When did the decagon form?
Astronomers first noticed a subtle undulating band in 2024. Ground-based imagery in 2025 strengthened the case, and a trawl back through the Hubble archive showed the pattern was already there in 2023.
Cassini is what makes the dating possible. It orbited Saturn from 2004 to 2017, roughly 13 years (the difference of those two dates), and photographed the planet more thoroughly than anything before or since. It saw nothing like this at the south pole.
So the decagon formed somewhere between 2017 and 2023, in the window after the orbiter was gone and before anyone from Earth thought to look closely.
Why did nobody see it happen?
Saturn sits about 1.4 billion km from the Sun on average, as astronomy references such as Universe Today give it, and no spacecraft has been watching it since Cassini ended its mission in 2017. The only regular eye on the planet is a telescope in Earth orbit, and it has a long list of other targets.
A feature the size of a continent grew on another planet, and the only reason we can put a date range on it is that Hubble happened to be pointing that way. Both Hubble and JWST, the James Webb Space Telescope, have further observations planned.
This is the kind of gap that survey instruments are built to close. Our piece on how the Roman Space Telescope compares with Webb explains why wide, repeated looks at the sky catch change that targeted observations miss.
Hubble's role matters here. It cannot match the close-up views that Cassini sent home, but it can return to the same planet again and again, and each visit adds a data point to the timeline. That repeat coverage is what turned a faint wavy band in 2024 into a confirmed decagon.
It also shows why archives are valuable. The 2023 images were taken for other reasons, and nobody studied them for this pattern until astronomers knew what to look for. Old data became the evidence that pinned down the date.
Is this the same story as the other Saturn decagon coverage?
Yes. We have also covered the finding from another angle in Saturn's famous hexagon has a bigger, weirder sibling at the opposite pole, which is worth reading alongside this one.
The sources for both are the same: NASA's Hubble release, Space.com and ScienceDaily. All three describe a ten-sided pattern, a 2017 to 2023 formation window and follow-up observations from Hubble and JWST.
Can you see Saturn's poles from home?
None of this is visible from a back garden. The polar shapes need a spacecraft or a space telescope, and an amateur instrument at best shows the disc, the rings and a handful of moons.
That is still worth doing. Saturn is well placed this autumn, and a steady pair of binoculars such as the Celestron Cometron 7x50 will show it as a distinctly non-round point of light, roughly what Galileo saw in 1610 before anyone worked out what the rings were. A small telescope resolves them properly.
For the view no telescope gives you, our piece on Webb's sharpest image of the Lion Nebula covers what happens when two instruments see the same object at different wavelengths. Another example of slow change caught by patient observation is Webb catching Chariklo's rings changing within five years.
What happens next?
The decagon is not necessarily stable. The northern hexagon has held for four decades, but a wave that appeared inside a six-year window could lose or gain sides inside one.
Hubble now has a baseline, so the next few years of imaging will show whether Saturn's south pole settled into a shape or is still working one out. If JWST adds infrared views, astronomers should also be able to see how deep into the atmosphere the pattern reaches.
For readers, the practical point is simple. Planetary atmospheres are not frozen, and a world that has been studied for decades can still change in ways that go unrecorded for years. Saturn is a reminder that continuous monitoring matters as much as any single mission.
Until then the honest answer to what caused it is that nobody knows. The dating is solid, the mechanism of a jet forced into a standing wave is well understood from the northern hexagon, and the trigger is the open question.
Key takeaways
- NASA published Hubble tracking on 3 September confirming a ten-sided jet pattern around Saturn's south pole.
- The decagon is a jet stream forced into a standing wave, and the northern hexagon has kept six sides since Voyager imaged it in 1981.
- Cassini saw nothing there before its mission ended in 2017, and Hubble archive images show the decagon by 2023.
- Astronomers first noticed the band in 2024, and ground-based imagery in 2025 strengthened the case.
- Both Hubble and JWST have follow-up observations planned to test whether the decagon is stable.
