At Saturn's south pole, a structure has appeared that astronomers have never seen there before. A giant ten-sided wave — a decagon — now encircles the planet's atmosphere, stretching through several of its layers. The Hubble Space Telescope has captured its clear outline, and scientists have traced how this shape gradually emerged and intensified starting in 2023.
For decades, Saturn's north pole has attracted attention with its famous hexagon — a stable atmospheric wave first spotted by the Voyager spacecraft in the 1980s and later studied in detail by Cassini. The south pole long remained without such geometry. Despite the symmetry of the planet's jet streams, searches for a southern counterpart, conducted since the 1990s, yielded nothing. Cassini data also showed no long-lived structure. And now it has appeared.
First, hints were picked up by ground-based observers. In 2024, on images collected through the Planetary Virtual Observatory Laboratory, Agustín Sánchez-Lavega, along with amateur astronomers Trevor Barry and Jean-Paul Auger, noticed a barely discernible wavy band near the south pole. By 2025, the signs became more confident. Then Hubble joined in as part of the OPAL program, which has been imaging the outer planets annually for over a decade. Its sharp images, free from Earth's atmospheric distortion, confirmed that the structure had existed at least since 2023 and was gradually becoming more pronounced.
The decagon sits within one of Saturn's powerful jet streams and extends vertically through different atmospheric levels. In Hubble's different filters, sensitive to different altitudes, its position shifts slightly — indicating that this is not a surface cloud feature but a true three-dimensional wave. It resembles the northern hexagon but also differs noticeably: that one has existed for over forty years and appears stable, while the southern decagon seems to be only now forming and strengthening before our eyes.
Amy Simon from Goddard Space Flight Center, a co-author of the study, notes: "We have never seen anything like this in Saturn's southern hemisphere. This structure appears to be intensifying, and we have a rare opportunity to observe the birth of a giant atmospheric pattern." Sánchez-Lavega adds that the search for a southern counterpart to the hexagon has been ongoing for a long time, but only now have Hubble's data confirmed it.
The results were published in the journal Science Advances. Next, scientists plan to monitor the decagon with Hubble and the James Webb Space Telescope to understand whether it will stabilize like the northern hexagon or continue to change. These observations could shed light on the dynamics of gas giant atmospheres in general — on how enormous planets, composed almost entirely of gas, can maintain regular geometric shapes for years.
Saturn continues to surprise. In its turbulent, chaotic atmosphere, an almost perfect decagon suddenly takes shape, as if invisible cosmic forces are imposing order on chaos. We live in a world where processes unfold hundreds of millions of kilometers away, reminding us how complex and coordinated the Universe is — and how much remains hidden from our eyes.
