Saturn Grew a Ten-Sided Storm Ring
Hubble has watched a decagon sharpen around Saturn's south pole. The ten-sided wave reaches through several atmospheric layers and appears to be new.
The Discovery
Saturn's north pole has worn a famous hexagon for more than four decades. Now its southern hemisphere has answered with a different piece of impossible-looking weather: a giant ten-sided wave wrapped around a jet stream.
A Science Advances study assembled Hubble images from the Outer Planet Atmospheres Legacy programme with observations contributed by astronomers on Earth. The feature was faintly present in Hubble data from 2023, became more apparent in 2024 and sharpened into a decagon during 2025.
Saturn has started drawing a new shape while we watch.
What Makes It Strange
Regular polygons in an atmosphere sound artificial, but rotating fluids can organise waves around fast jets. Saturn's northern hexagon is the classic example. The southern structure is not simply its mirror.
- It is the first large regular-sided jet pattern identified in Saturn's southern hemisphere.
- Different Hubble wavelengths detect it at different heights.
- Cassini observations from 2004 to 2017 showed no comparable long-lived southern feature.
- The decagon appears to be strengthening rather than sitting in a settled state.
According to NASA's Hubble report, the vertical reach means this is not a decorative line of cloud tops. It is an atmospheric structure with depth.
The Implications
The discovery gives planetary scientists something rare: a possible polygonal jet wave caught during formation. Comparing its growth with the stable northern hexagon can test how season, wind shear and surrounding storms organise gas-giant atmospheres.
The trigger is not established. Saturn's changing seasons recently returned the south pole to a useful viewing angle from Earth, so the record still leaves two possibilities: a genuinely recent formation or an earlier stage hidden by geometry and sparse observations.
What Happens Next
Hubble and Webb can follow the wave through new seasons and at different atmospheric depths. Models then have to reproduce ten corners, the surrounding jet and the structure's evolution without pretending a striking shape is an explanation.
The hexagon looked like Saturn's signature. The planet has started revising it.