Future TechnologySaturn'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
104,000 miles across, 10 sides, and still growing. That is the feature the Hubble Space Telescope has confirmed at Saturn's south pole, described in a paper published in Science Advances on 2 September.
Saturn's north pole has had a hexagonal storm for over 40 years. Six sides, roughly 20,000 miles wide, sitting at the cloud tops. Planetary scientists spent decades trying to explain it. The southern decagon is something else entirely.
What Hubble found
The Saturn south pole decagon is an atmospheric wave, not a single storm. It encircles the pole as a standing wave pattern with 10 distinct sides and extends through multiple layers of the atmosphere rather than sitting at a single altitude. Hubble first detected it forming in 2023, and three years of observations show it has been growing stronger and more defined over time.
The paper's lead author used ultraviolet and visible light imagery from Hubble's Wide Field Camera 3 to map the feature's evolution. The wave pattern appears where fast-moving gas at lower latitudes meets slower-moving gas near the pole, creating a boundary that folds into a geometric shape.
Why ten sides is 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, so the hexagon at least 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, possibly linked to Saturn's seasonal cycle as its south pole enters a long summer.
For a sense of how different telescopes reveal different phenomena in the same targets, our explainer on the water signature near the Milky Way's black hole covers how JWST and Hubble see the universe in complementary ways.
Geometry where you would not expect it
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.
Saturn's south pole is now the second confirmed geometric feature on the planet, and the two shapes are different in almost every way: number of sides, vertical extent, age, and growth behaviour. That tells its own story about what we still do not understand about the planet we have been studying longest.
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. That has implications for how we model atmospheres on gas giants here and on the growing catalogue of exoplanets being observed by JWST.
Venus is still producing tectonic surprises too. The solar system keeps reminding us how much basic planetary science remains unsettled.
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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