Saturn's famous hexagon has a bigger, weirder sibling at the opposite pole
Key takeaways
- Hubble confirmed a 10-sided geometric wave encircling Saturn's south pole, roughly 104,000 miles across
- The feature was first detected in 2023 and has been growing stronger over three years of observations
- Saturn's northern hexagon has persisted for 40 years, but the southern decagon is structurally different in almost every way
- No single accepted model explains why gas giant atmospheres produce geometric shapes
The Hubble Space Telescope has confirmed a 10-sided wave pattern, roughly 104,000 miles across, encircling Saturn's south pole, and it is still growing. The finding is described in a paper published in Science Advances on 2 September.
Saturn's north pole has carried a hexagonal storm for over 40 years. It has six sides, is roughly 20,000 miles wide and sits at the cloud tops. Planetary scientists have spent decades trying to explain it. It was first imaged by the Voyager spacecraft in the early 1980s and later studied up close by Cassini, so researchers have had a long time to build theories around it. The southern decagon turns out to be something else entirely, and it does not fit those theories neatly.
That contrast is the reason the new result matters. A second polygon at the opposite pole gives scientists a test of whether their explanations for the first one hold up.
What did Hubble find at Saturn's south pole?
The Saturn south pole decagon is an atmospheric wave, not a single storm. It encircles the pole as a standing wave pattern (a wave that holds its shape rather than travelling) with 10 distinct sides. It also extends through multiple layers of the atmosphere rather than sitting at a single altitude.
Hubble first detected it forming in 2023. Three years of observations show it has been growing stronger and more defined over time, which is part of what makes it so interesting to researchers.
The paper's lead author used ultraviolet and visible light imagery from Hubble's Wide Field Camera 3 to map the feature's evolution. Using both kinds of light lets astronomers see features at different heights, because haze and gas absorb and scatter each wavelength differently.
How does the wave form?
According to NASA's account of the work, the wave pattern appears where fast-moving gas at lower latitudes meets slower-moving gas near the pole. That contrast creates a boundary, and the boundary folds into a geometric shape instead of staying a smooth circle.
Think of a flag flapping in the wind. The cloth ripples because two layers of air move at different speeds along its edge. Saturn's version works on a planetary scale, with a polar region whose gas moves at a different pace from the belts around it.
This is why scientists describe the feature as a wave and not a vortex. A vortex is a spinning storm with a core. A wave is a pattern in a flow, and the pattern can have many sides without any single storm sitting at its centre.
Why is ten sides stranger than six?
The northern hexagon was puzzling enough. Fluid dynamics experiments in spinning tanks showed that you can produce hexagonal patterns when a jet stream is sandwiched between two regions of different rotation speeds. The hexagon therefore had a plausible laboratory analogue.
A decagon is harder to explain. More sides means the wave pattern has a higher mode number, which requires more specific conditions to form and sustain. The fact that it is growing rather than decaying suggests the conditions driving it are intensifying.
One possible link is Saturn's seasonal cycle, as its south pole enters a long summer. According to NASA, Saturn takes about 29.5 years to orbit the Sun, so each season lasts roughly seven years. That is a hypothesis rather than a result, and the paper does not settle it.
How do the two Saturn polygons compare?
The two shapes share a planet and little else. The table sets out what is known from the Hubble work and the decades of earlier observation of the north.
| Feature | North pole hexagon | South pole decagon |
|---|---|---|
| Number of sides | 6 | 10 |
| Width | Roughly 20,000 miles | Roughly 104,000 miles |
| Age | Over 40 years | First detected in 2023 |
| Vertical extent | Sits at the cloud tops | Extends through multiple atmospheric layers |
| Trend | Persistent | Growing stronger and more defined |
| Laboratory analogue | Yes, in spinning tank experiments | Harder to explain |
Saturn's south pole is now the second confirmed geometric feature on the planet. The differences run through number of sides, vertical extent, age and growth behaviour. That tells its own story about how much we still do not understand about the planet we have been studying longest.
Our earlier piece on how Saturn grew a decagon at its south pole while nobody watched covers the first signs of the feature in more detail.
Do other planets have geometric shapes?
Geometric patterns in planetary atmospheres should not work, but they keep showing up. Jupiter has polygonal structures at its poles too, captured by the Juno spacecraft. Understanding why gas at planetary scale settles into geometric shapes, instead of the turbulent swirls you might expect, is one of the open problems in atmospheric dynamics.
No single accepted model explains why gas giant atmospheres produce these shapes. The decagon adds a data point to a very small dataset. If the same planet can produce a hexagon at one pole and a decagon at the other, the underlying mechanism is more flexible than current models assume.
Why does it matter beyond Saturn?
Atmospheric models built for gas giants in our own solar system are also used to interpret the growing catalogue of exoplanets being observed by JWST. A model that cannot explain a ten-sided wave next door is on shaky ground when asked about a world light-years away. For a sense of how that telescope sees things Hubble cannot, our explainer on the water signature near the Milky Way's black hole shows how the two observatories complement each other.
Hubble's role here is worth appreciating. It has been in orbit for decades, yet it is still the instrument that can watch a slow change at Saturn over three years with consistent ultraviolet and visible imaging. Long, steady baselines are exactly what a slowly growing wave needs.
The wider solar system keeps reminding us how much basic planetary science remains unsettled. Venus is still producing tectonic surprises too, and the Webb telescope has watched Chariklo's rings changing within five years.
What happens next?
The obvious question is whether the decagon keeps growing or settles into a stable shape. Further Hubble observations should show whether it strengthens through Saturn's long southern summer, and whether it ever reaches a size or form comparable with the northern hexagon. Neither outcome has been reported yet.
If you want to observe Saturn yourself while the south pole is well positioned, a pair of astronomy binoculars will show the rings and the planet's disc clearly, though resolving atmospheric detail requires a telescope.
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