A team of astronomers has identified a polygonal atmospheric structure on Saturn near the planet's south pole. This 10-sided shape, known as a decagon, adds to the gas giant's notable features, including a hexagon observed near the north pole 44 years ago. Images of the decagon were obtained using the Hubble Space Telescope, with the findings published in the journal Science Advances.
The formations at both poles are not solid structures, as Saturn lacks a defined solid surface like Earth. Descending through Saturn's atmosphere would result in increasing pressure and density without reaching a solid ground. The observed patterns are formed by clouds, which are notably unusual.
Each side of the decagon measures approximately 16,800 kilometers, exceeding Earth's diameter by several thousand miles. Adjacent to the feature is a jet stream with speeds of 116 meters per second, or nearly 260 miles per hour. In comparison, a Category 5 hurricane on Earth has winds exceeding 157 miles per hour. Despite the high speed of the jet stream, the decagon pattern shifts at only 2.5 meters per second, or less than 6 miles per hour.
The south pole feature appears to have formed recently. For decades, scientists sought a counterpart to the northern hexagon, but previous missions had not identified a similar long-lasting structure in the south. Observations were complicated by Saturn's tilt, which obscured its southern hemisphere from Earth for many years.
Initial clues about the decagon came from ground-based observations, including those by amateur astronomers. As more images were collected, it became clear that an unusual phenomenon was occurring in Saturn's southern cloud bands. Data from the Hubble Space Telescope allowed researchers to trace the pattern back to images taken in 2023. Continued monitoring revealed that by 2025, the decagon's 10 vertices were more distinctly defined, confirming the presence of this new polygonal feature in Saturn's atmosphere. The scientific community has yet to reach a consensus on the formation of these structures.
Several hypotheses have emerged since the discovery of the northern hexagon. One theory suggests that the polygons are visible manifestations of large atmospheric waves confined by strong jet streams. These waves can be likened to ocean waves, which are disturbances propagating through water rather than mere objects traveling across it.
The behavior of a wave varies based on the environment and boundaries it encounters. On Saturn, atmospheric gas waves may interact with jet streams that confine them, akin to a beach's edge. However, in this case, the "beach" encircles the entire planet.
Other factors, including Saturn's rapid rotation, specific wind speeds, and variations in currents, may also influence the unique geometries of these shapes. A current that coils around the planet six times can create a hexagon, while one that coils ten times can form a decagon. This explanation is among the more plausible for how a gaseous atmosphere can produce a large polygonal appearance, but many questions remain unanswered.
Researchers are uncertain about the depth of these geometric figures, the longevity of the new decagon, whether its formation is related to Saturn's seasons, and what triggered its emergence. To seek answers, astronomers plan to continue observing the decagon's evolution using the Hubble and James Webb space telescopes, along with advanced atmospheric models to reconstruct conditions that could lead to such a structure.