Hubble’s 29 August 2025 observation and a polar projection. The central marked area lacks usable image data. Original image. Credit: NASA, ESA, STScI, A. Sánchez-Lavega (University of the Basque Country), A. Simon (NASA-GSFC), M. Wong (UC Berkeley); Image Processing: A. Pagan (STScI). CC BY 4.0.
The Saturn decagon is a ten-sided atmospheric wave around the planet’s south pole. Hubble observations show an evolving pattern on a world we thought we recognised: pale bands, spectacular rings and weather that still has surprises in store.
On 2 September 2026, ESA announced that Hubble observations had revealed an evolving, ten-sided atmospheric wave around Saturn’s south pole. Researchers traced evidence back to 2023. It occupies a jet stream and appears to extend through several atmospheric layers. ESA’s discovery report
A ten-sided shape is called a decagon. Here, the geometry describes moving weather. Imagine a ribbon of cloud wrapped around a pole, with a repeating series of bends. The fascinating thing is that flowing material can organise itself into something our eyes associate with a drawing made using a ruler.
How the Saturn decagon differs from the northern hexagon
The planet’s northern hexagon has six sides and a much longer observational history. Voyager saw it in the early 1980s, and Cassini later examined its motion. NASA describes laboratory experiments in which rotating fluids develop polygonal patterns when neighbouring regions move at different speeds. Orderly shapes can emerge naturally from fluid motion. NASA’s explanation of the northern hexagon
That context is useful without being a complete explanation of the new discovery. A six-sided structure at one pole does not tell us automatically why ten bends should appear at the other. A successful explanation has to account for the details, not just produce a vaguely similar shape.
Saturn’s seasons also move on a very different clock. One orbit takes roughly 29 Earth years, so a season lasts more than seven. Cassini used infrared observations to examine the northern hexagon during winter darkness before sunlight returned. A planet can be changing while our ability to see that change also changes. Cassini’s changing view
The archive became part of the discovery
Amateur observations helped draw attention to the southern pattern in 2024 and 2025. Researchers then used Hubble’s archive to investigate its earlier development. The absence of a comparable long-lived feature in Cassini’s observations does not establish an exact formation date. Its origin and likely lifetime remain open questions. How the evidence came together
This is one reason repeated observations matter. A single striking photograph shows what a planet looked like at one moment. A sequence can reveal whether a feature strengthens, fades or changes with the seasons.
Hubble’s Outer Planet Atmospheres Legacy programme, known as OPAL, regularly observes Jupiter, Saturn, Uranus and Neptune. NASA describes the programme as a way to build a consistent record of atmospheric behaviour across years. Its images provide context that individual spacecraft encounters cannot supply on their own. NASA on a decade of OPAL observations
The payoff is easy to appreciate. If you want to understand a storm, one photograph is a start. If you want to understand how an entire weather system changes, you need a record you can keep returning to.
What happens next to the Saturn decagon?
Future observations and modelling should help establish whether the wave settles into a persistent pattern or continues to evolve. The discovery team identifies further Hubble and Webb work as part of that effort. The proposed next steps
For readers drawn to the strange worlds beyond Earth, this sits alongside discoveries such as planets travelling without a sun: familiar words can conceal unfamiliar physics.
Saturn has been photographed for generations. Its new weather pattern is a reminder that knowing where a planet is, and recognising its silhouette, are only the beginning of understanding what it is doing.
Leave a Reply