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Saturn is generally acknowledged as the most beautiful planet in the solar system (excepting Earth), but it’s also one of the weirdest. It has gigantic rings! A fleet of bizarre moons! A very strange and borderline eerie hexagon at its north pole!

And now it only gets weirder: using images taken by Hubble Space Telescope, astronomers have spotted a polygonal structure at Saturn’s south pole. And it’s not any ordinary shape, like a square or a pentagon. It’s a decagon.

The edges aren’t perfectly distinct, but there are ten sides there [link to journal paper]. So, what the heck is going on?

Physics! And fluid dynamics!

These structures are due to a phenomenon called Rossby waves, and come about naturally when you have two adjacent fluids moving at different speeds on a rotating planet. As the outer one moves around the inner one, they interact and create regular polygonal shapes. The number of sides (and the length of each side) depends on a lot of factors, like the relative speed, how fast the planet is spinning, and so on. 

This seems counterintuitive, but there’s a great video showing this exact thing occurring in a lab setting. They put two fluids on a rotating table and mounted the camera above the table and rotating with it, and you can see the hexagon (six-sided figure) forming:

See? And remember, gas is a fluid; anything that flows is a fluid, and that includes liquids and gasses. Incidentally, Jupiter has similar structures, with five immense cyclones circling a central cyclone at its south pole. The underlying physics is similar. Neptune might have a hexagon at one of its poles as well.

The decagon at Saturn’s austral pole is persistent, in that it’s existed for several years at least. It was seen in Hubble images starting in 2023, and was still there in late 2025. It may be older than that, too. The Cassini spacecraft saw a partially formed polygon in 2004, but it didn’t last, so this feature didn’t exist 20 years ago.

Spotting it from Earth is hard because a) it’s at the pole which we can’t see from above, and 2) Saturn has an axial tilt similar to Earth’s, and it’s been austral winter since 2012, with the pole pointing away from the sun (and us). It was only in 2023 that the pole swung back into view and Hubble could see it.

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So how do we get a Hubble image from above then? We don’t, not really. The image is actually a mosaic made from several observations, all of which show the pole from a shallow angle at different parts of Saturn’s day (as shown in the top part of the image above). Over time the whole decagon was seen, and astronomers could create a mosaic of it unrolled, like it had been peeled off Saturn and laid flat (astrophotographer Damian Peach did this in a cool image of Jupiter as an example). From there you can use geometry and map projection to reconstruct the image as if it’s seen from above. I’ve done similar processing myself to look at circular structures and be able to analyze them more easily.

The decagon is huge, too. Each side is nearly 17,000 kilometers long — Earth is about 13,000 km in diameter, for comparison, so our entire planet could pass easily through one side of this structure without touching the vertices.

The astronomers point out that there’s a big anticyclonic storm near the decagon (not seen in this image) that may play a role in its formation, though how isn’t clear. While the overall physics of these kinds of features is understood, the details are incredibly complex. 

I remember back in 2012 when the hexagon at Saturn’s north pole was clearly seen in Cassini images, and being really amazed. Of course some people cried “aliens” — some people always do, even without, y’know, evidence — but in my opinion that shows a lack of imagination. It’s easy to simply say aliens did something. The hard part is showing how nature might be able to do it.

And here we have exactly that. Nature is clever, more clever than we are, in that it can still surprise us by creating structures we may not have expected. But once we see them, study them, we can apply our scientific knowledge to them and explain them. That’s why science will always be cooler than pseudoscience.

Did you ever wonder how real scientists are searching for alien life? What they look for in exoplanets, and how they can determine what’s going on in a world a quadrillion kilometers away?

I’m moderating a panel of real astrobiology scientists called “Strange New Worlds: The Science of Star Trek”, hosted by the Carnegie Science Earth and Planets Laboratory on Wednesday, September 9, 2026. Panelists include Mike Wong, Maggie Thompson, and Nicole Wallack. We’ll be talking about alien planets in the context of Star Trek, comparing the fact and fiction while nerding out about both.

The panel will be at 6:30 p.m. at the Greenwalt Lecture Hall in Washington DC. It’s free, but you need to register so they get a head count. There will be a live stream, too.

All the info you need is on their web page for the event. I hope y’all can come!

You can email me at [email protected] (though replies can take a while), and all my social media outlets are gathered together at about.me. Also, if you don’t already, please subscribe to this newsletter! And feel free to tell a friend or nine, too. Thanks!