Saturn’s Southern Decagon: A Newly Discovered Ten-Sided Atmospheric Wave

Astronomers have identified a giant, ten-sided wave—dubbed the “decagon”—encircling Saturn’s south pole. The feature first appeared in Hubble Space Telescope images taken in 2023 and became clearly defined in observations obtained on August 29 2025. The decagon lies near 60° south latitude, rides an eastward jet stream, and extends through multiple atmospheric layers, indicating it is more than a surface cloud pattern.

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Saturn’s north pole hosts a six-sided hexagonal jet stream discovered by Voyager in 1980–81. Because Saturn’s axial tilt (? 26.7°) hides the southern hemisphere for long intervals, no comparable southern polygon was seen in Cassini data (2004–2017) or earlier Hubble images. As the planet moved toward southern spring, the pole re-entered view, allowing observers to notice a faint undulating band in 2024. The Hubble Outer Planet Atmospheres Legacy (OPAL) program then captured higher-resolution data that confirmed the decagon’s presence.

NASA's Cassini spacecraft circled Saturn for 13 years and never saw a shape at the south pole, but when the planet's slow seasons tilted that pole back toward Earth, a giant ten-sided figure was waiti Hubble tracks new decagon encircling Saturn’s south pole Science DailySpace.comScienceAlert

• Overall width: ? 104,250 mi (167,820 km) across the ten sides.

NASA's Cassini spacecraft circled Saturn for 13 years and never saw a shape at the south pole, but when the planet's slow seasons tilted that pole back toward Earth, a giant ten-sided figure was waiti

• Side length: each side ? 10,425 mi (16,782 km).

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• Rotation period: about 800 days for a full circuit.

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• Drift speed: roughly 10 km h?¹ (? 6 mph) eastward, far slower than the jet stream’s ? 420 km h?¹.

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• Latitude band: 58°–63° south.

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• Vertical extent: multi-wavelength observations show the pattern at different altitudes.

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Study lead author Agustín Sánchez-Lavega (University of the Basque Country) said the decagon demonstrates Saturn’s ability to generate polygonal waves in both hemispheres, challenging the view that the hexagon is unique. Co-author Amy Simon (NASA Goddard) noted the feature appears to be strengthening, offering a rare chance to watch a giant atmospheric pattern develop in real time. Researchers highlighted seasonal insolation—solar heating will peak near the decagon’s latitude around 2032—as a factor that may influence its evolution.

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Sources differ on several quantitative details:

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• Formation window: some analyses place emergence between 2017 and 2023, while others cite a clear Hubble capture only in 2023.

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• Drift speed: one report lists 6 mph (10 kph), another ? 10 km h?¹. Both describe slow eastward motion relative to the jet stream.

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• Stability: darkness varies across sides, suggesting ongoing evolution; long-term persistence remains unknown. Continued monitoring is required.

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• “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

Hubble tracks new decagon encircling Saturn’s south pole

• “We’ve never seen anything quite like this in Saturn’s southern hemisphere,” — Amy Simon

Hubble tracks new decagon encircling Saturn’s south pole

The team will continue Hubble observations and incorporate data from the James Webb Space Telescope to track changes in the decagon’s shape, speed, and vertical structure. As solar insolation peaks near the feature’s latitude around 2032, scientists will assess whether increased heating stabilizes the wave or leads to its breakup. The study was published in *Science Advances* on September 2.

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