Scientists have identified a massive, 10-sided wave pattern swirling in the icy ammonia clouds above Saturn's south pole. This newly discovered decagon jet stream appears to be larger and more unstable than the famous hexagon of clouds circling the planet's north pole, which was first observed by NASA's Voyager spacecraft in the 1980s.
The decagon was detected in images captured by the Hubble Space Telescope in 2023. Researchers suspect the formation may have emerged between 2017 and 2023, during a period when Saturn's south pole was tilted away from Earth and unobservable. The phenomenon may still be evolving, with individual sides of the decagon already spanning over 10,000 miles (16,700 kilometers).
Lead author Agustin Sanchez-Lavega of the University of the Basque Country stated that the discovery indicates the "unique" hexagon is not as extraordinary as previously thought. The findings were published in the journal Science Advances.
While atmospheric wave disturbances are common on planets with atmospheres throughout the solar system, Saturn is unique in producing these disturbances in polygonal shapes. Both the decagon and the hexagon are situated on jet streams. However, the northern hexagon remains nearly stationary, while the southern decagon drifts eastward at approximately 6 mph (10 kph).
Comparing these two formations at opposite poles could offer valuable insights into the weather patterns of giant gas planets, according to Sanchez-Lavega. "This is a highly interesting phenomenon that appears to be unique to Saturn, and we want to know why," he said.
Sanchez-Lavega also raised the possibility that these formations might be related to the polygonal cyclones observed on Jupiter. Improved observation of Saturn's southern hemisphere in the coming years is expected to provide more details about the decagon and potentially resolve this atmospheric mystery.
It remains uncertain whether the decagon will persist as long as the hexagon, which has been visible for over 40 years, a duration longer than a single Saturnian year (equivalent to 30 Earth years). "For the time being, all I can confirm is that the decagon is still there," Sanchez-Lavega noted.