A 10-sided atmospheric wave, or decagon, has been observed encircling Saturn’s south pole for the first time, with NASA’s Hubble Space Telescope confirming its presence since 2023. Unlike Saturn’s long-standing hexagon in the north, the decagon appears to be a relatively new feature, offering scientists a rare chance to study a giant weather system in real time.
The decagon, a polygonal structure with 10 sides, was first detected in 2023 through a collaboration between amateur and professional astronomers. Ground-based observations in 2024 and 2025 revealed its gradual emergence, while Hubble’s high-resolution imaging confirmed its existence within Saturn’s atmosphere. The feature, spanning 104,250 miles (167,820 kilometers) across, is embedded in one of Saturn’s powerful jet streams and extends through multiple atmospheric layers, suggesting it is not merely a surface-level cloud pattern.
A New Meteorological Puzzle
We’ve never seen anything quite like this in Saturn’s southern hemisphere,
said Amy Simon, a study co-author and principal investigator with NASA’s Goddard Space Flight Center. The decagon’s discovery challenges previous assumptions about Saturn’s atmospheric symmetry, as scientists had long searched for a counterpart to the northern hexagon, which has remained stable for over 40 years. Unlike the hexagon’s uniform structure, the decagon exhibits varying darkness across its edges, hinting at an evolving, dynamic system.
Agustín Sánchez-Lavega, lead author of the study from the University of the Basque Country, noted that the decagon’s formation may be linked to a meandering wave trapped within Saturn’s jet stream. Computer simulations suggest the shape could arise from disturbances in the jet or interactions with nearby atmospheric features. The most intriguing part to me is that this seems to have just formed recently,
Sánchez-Lavega said, emphasizing the rarity of observing such a phenomenon in real time.
Comparing the Decagon and the Hexagon
Saturn’s northern hexagon, first observed in 1988, is a well-documented feature that has remained largely unchanged for decades. In contrast, the southern decagon appears to be in a transitional phase. While the hexagon’s sides have maintained consistent contrast, the decagon’s edges vary in darkness, suggesting it may still be evolving. This feature is different—it appears to be strengthening, giving us the rare opportunity to watch a giant atmospheric pattern develop,
Simon said.
The decagon’s rotation period is approximately 800 Earth days, slower than the northern hexagon’s pace. Scientists are using Hubble and the James Webb Space Telescope to track its changes, aiming to determine whether it will become a permanent feature or dissolve over time.
Implications for Atmospheric Science
The discovery of the decagon provides insights into the mechanisms driving large-scale weather patterns on gas giants. Researchers hope to apply these findings to better understand Earth’s atmospheric dynamics. This is a very unusual atmospheric phenomenon that is helping us to advance our understanding of meteorology in general,
Sánchez-Lavega said. The study, published in Science Advances, highlights the importance of long-term observational programs like NASA’s Outer Planet Atmospheres Legacy (OPAL), which has tracked Saturn’s atmosphere for over a decade.
Amateur astronomers played a critical role in identifying the decagon, with contributions from Trevor Barry and Jean-Paul Oger. Their ground-based observations, combined with Hubble’s data, allowed scientists to trace the feature’s emergence back to 2023. We’ve been searching for a counterpart to Saturn’s northern hexagon on the south pole in Hubble images since 1990,
Sánchez-Lavega said, noting that previous missions like Cassini found no evidence of a similar structure.
As scientists continue to monitor the decagon, questions remain about its longevity and the factors driving its formation. We need to understand how the decagon evolves—whether in the coming years it will become unstable and break up, or conversely, become more stable and robust as solar radiation increases,
Sánchez-Lavega explained. The study underscores the value of combining amateur and professional efforts in planetary science, offering a new chapter in the exploration of Saturn’s mysteries.
