The Planet's Famous Six-Sided Storm
Since NASA's Voyager spacecraft flew by Saturn in the early 1980s, astronomers have been captivated by its northern hexagon. It is a colossal jet stream, a river of air whipping around the pole at hundreds of kilometres per hour, locked into a remarkably
stable six-sided shape. Each side of the hexagon is wider than Earth itself, and for over 40 years, it has remained a permanent and perplexing fixture of the gas giant. Scientists believe it to be a type of massive atmospheric phenomenon known as a Rossby wave, a pattern that also appears in Earth's atmosphere and oceans. Laboratory experiments have even managed to recreate similar polygonal shapes in spinning tanks of liquid, but Saturn's hexagon has remained the solar system's most spectacular example of geometric weather. Its sheer persistence led many to wonder if a similar feature existed at the planet's south pole.
A Surprise Discovery in the South
For years, the answer was no. NASA’s Cassini spacecraft orbited Saturn from 2004 to 2017, studying the planet in unprecedented detail. While it gathered stunning data on the northern hexagon, it found no such stable, geometric shape in the south. But in a dramatic turn, recent observations have revealed that has changed. Using images from the Hubble Space Telescope, a team of researchers has confirmed the emergence of a brand new feature: a ten-sided decagon circling the south pole. The discovery, announced in early September 2026, was made possible by the Outer Planet Atmospheres Legacy (OPAL) program, which regularly monitors the solar system's giants. Interestingly, the first clues came from amateur astronomers who noticed faint undulations in ground-based images starting in 2024, prompting a closer look with Hubble.
An Unstable, Evolving Mystery
While both are polar storms, the southern decagon is profoundly different from its northern sibling. The most obvious distinction is its shape, with ten sides instead of six. But the crucial difference is its age and stability. Where the hexagon is ancient and unchanging, the decagon is a newborn. Scientists have traced its origins back to Hubble images from 2023, but it was not present during the entire Cassini mission, which ended in 2017. This means the decagon formed recently and is still evolving, with observations suggesting it is growing stronger and more defined. This gives scientists something they never had with the hexagon: the chance to watch a planetary-scale polygonal storm form and develop in near real-time. The winds associated with the decagon are also different, gusting at around 400 kilometres per hour, slightly faster than the hexagon's jet stream.
Why Now, and Why Different?
The sudden appearance of the decagon raises fascinating questions. Why would one pole host a stable, 40-year-old hexagon while the other suddenly sprouts a decagon? Scientists are working on the puzzle, but early theories suggest a nearby vortex, or smaller storm, may have acted as a trigger, perturbing the jet stream and forcing it into its ten-sided shape. Saturn has seasons, much like Earth, though they last over seven years each. The planet's tilt meant its south pole was hidden from our view for many years, only recently coming back into sight. The decagon’s formation during this period highlights just how dynamic and changeable the atmospheres of these giant planets can be. What once seemed like a symmetrical system, with scientists expecting to find a southern hexagon, has turned out to be far more complex and interesting.
A Front-Row Seat to Planetary Science
For planetary scientists, this discovery is more than just a cosmic curiosity. It's a natural laboratory for understanding the physics of planetary atmospheres. By monitoring the decagon's evolution, they can test theories about how these gigantic, long-lasting storms are born and what keeps them stable. The insights gained could help explain the dynamics not only on Jupiter, which has its own cluster of polar cyclones, but also potentially refine our understanding of atmospheric physics here on Earth. The northern hexagon has always been a static mystery, a finished puzzle. The new southern decagon, however, is a story that is just beginning to unfold, offering a rare and invaluable window into the powerful forces that shape alien worlds.
