Astronomers using the Hubble Space Telescope have discovered a massive 10-sided atmospheric wave, or decagon, encircling Saturn’s south pole. First appearing in data from 2023, the unique polygonal jet stream challenges long-held assumptions about gas giant atmospheres and provides researchers a rare chance to watch a giant weather pattern evolve.
Saturn is famous for its serene, banded appearance and ferocious winds that whip up to 500 miles per hour. Beneath that calm exterior, however, the ringed planet hides bizarre geometry. More than four decades ago, NASA’s Voyager probes spotted a famous six-sided hexagonal jet stream locked around Saturn’s north pole. That northern feature remained a solitary planetary curiosity for over 40 years, baffling scientists who searched in vain for a southern counterpart.
That search finally paid off when archival data and high-resolution space imagery revealed an entirely different polygonal formation taking shape on the opposite end of the planet. Researchers published the discovery in the journal Science Advances.
Spotting the Decagon: From Ground-Based Hints to Hubble’s Sharp View
The discovery began on the ground before moving into space. Agustín Sánchez-Lavega of the University of the Basque Country in Spain, working alongside amateur astronomers Trevor Barry and Jean-Paul Oger, first noticed a subtle undulating band in southern polar images. They utilized the university’s Planetary Virtual Observatory Laboratory, an online platform that aggregates observations of solar system planets captured by skywatchers around the globe.
Additional imagery captured from the ground in 2025 provided stronger hints that the wavy band formed a distinct decagonal shape. To clear away the atmospheric blur of Earth, researchers turned to space.
Observations from the Hubble Space Telescope confirmed the feature’s presence dating back to 2023, showing that the structure had begun emerging just as Saturn’s changing axial tilt brought the southern pole back into view. Saturn’s south pole was tilted away from Earth and therefore out of view between 2017 and 2023.
“Given Saturn’s symmetry in its north-south jet stream system, we have been searching for a counterpart to Saturn’s northern hexagon on the south pole in Hubble images since 1990.”
Agustín Sánchez-Lavega, University of the Basque Country
Crucially, data from NASA’s Cassini spacecraft, which orbited the gas giant between 2004 and 2017, showed no inkling of a long-lived formation during its mission lifetime. This timeline indicates the decagon likely formed sometime between 2017 and 2023.
How the Southern Decagon Differs From the Northern Hexagon
While both geometric formations sit atop powerful jet streams, the newly found southern decagon behaves quite differently than its northern sibling. The northern hexagon is practically stationary, whereas the southern decagon migrates eastward at a tame pace of roughly 6 miles per hour.
Size is another major differentiator. A single side of the sprawling decagon already surpasses 10,000 miles in length. Furthermore, Hubble observations demonstrate that the decagon extends vertically through multiple layers of the atmosphere, proving it is far more than a shallow, cloud-level feature.
“The northern hexagon has been there every time we’ve looked for more than 40 years. This feature is different — it appears to be strengthening, giving us the rare opportunity to watch a giant atmospheric pattern develop.”
Amy Simon, NASA’s Goddard Space Flight Center
What Comes Next for Saturn’s Mysterious Wave
The sudden appearance of the decagon forces a reassessment of planetary weather. Rather than viewing Saturn’s northern hexagon as an isolated anomaly, researchers now recognize that the planet’s atmospheric conditions routinely foster polygonal waves in both polar regions.
Whether the southern decagon will endure for decades like the northern hexagon remains an open question. Researchers point out that the southern feature appears more unstable and prone to change.
To solve the mystery, scientists plan to combine computer simulations with fresh observations. Researchers will rely on scheduled time with the Hubble Space Telescope and target observations using the James Webb Space Telescope to monitor how the wave generates, what triggers its sharp angles, and whether it will eventually stabilize.
