A New Shape on an Old Friend
Saturn has long been defined by its majestic rings, but planetary scientists have been equally fascinated by a feature at its north pole: a colossal, six-sided jet stream known as "the hexagon." This storm has been a stable, perplexing fixture for over
40 years since it was first seen by the Voyager spacecraft. Scientists long wondered if a similar structure existed at the planet's south pole. Now, they have an answer, and it is not what they expected. Recent observations have revealed a giant, 10-sided atmospheric wave—a "decagon"—circling the southern pole. This discovery, published in the journal Science Advances, confirms that Saturn has a penchant for polygons, but its two poles tell very different stories. Unlike the long-lived hexagon, the southern decagon appears to be a recent and evolving phenomenon, giving scientists a rare ringside seat to the birth of a planetary-scale weather system.
An Eye in the Sky
Spotting this new feature was a matter of patience and persistence. The discovery was made using images from the Hubble Space Telescope's Outer Planet Atmospheres Legacy (OPAL) program, which annually captures detailed portraits of our solar system's gas giants. For over a decade, from 2012 to 2023, Saturn's south pole was tilted away from Earth's view, hiding whatever might be brewing there. As the pole gradually came back into view, astronomers began to see hints of something unusual. Faint signs of the decagonal structure were found in Hubble data going back to 2023. These hints were first noted by a team led by Agustín Sánchez-Lavega, which collaborates with amateur astronomers who contribute ground-based observations. The pattern became more defined throughout 2024 and 2025. The timing is crucial; NASA's Cassini spacecraft, which orbited Saturn from 2004 to 2017, saw no evidence of such a long-lived structure, suggesting the decagon formed sometime after Cassini's mission ended.
More Than Just Cloud-Deep
The headline's mention of "multiple atmospheric layers" points to one of the most significant aspects of the discovery. This is not just a pattern painted on the cloud tops. By observing Saturn at different wavelengths of light, Hubble was able to probe different altitudes in its atmosphere. The decagonal wave was found to extend vertically through these layers, indicating it is a deep and robust atmospheric structure. This three-dimensional nature is similar to the northern hexagon and suggests it is a powerful wave embedded within one of Saturn's powerful jet streams, which can whip around the planet at speeds over 400 kilometers per hour. This depth is what makes these polygonal storms so different from a typical hurricane on Earth; they are features tied to the fundamental dynamics of the planet's deep atmosphere.
An Unfolding Mystery
The discovery of the decagon raises more questions than it answers. Chief among them is: why now? "The most intriguing part to me is that this seems to have just formed recently," said Amy Simon, a study co-author and NASA scientist. While the northern hexagon has been a picture of stability for decades, the southern decagon is a dynamic newcomer. Scientists are now working to understand the forces that could create such a massive and orderly geometric shape. Computer simulations suggest it might have been triggered by a disturbance in the jet stream, perhaps related to a nearby swirling vortex storm, but no model has yet been able to fully reproduce the 10-sided pattern. The differences in the number of sides—six versus ten—and their relative stability are key puzzles that will help scientists refine their models of how gas giant atmospheres work.
