A 'Decagon' Has Appeared
The biggest news from Hubble is the confirmation of a massive, 10-sided atmospheric wave encircling Saturn's south pole. Dubbed a "decagon" by astronomers, this is the first time any large, regular-sided jet pattern has been observed in the planet's southern
hemisphere. While Saturn's north is famous for its hexagon, this southern counterpart introduces a new geometric puzzle. The feature is embedded in one of the planet's powerful jet streams, a fast-moving river of air that shapes the weather on this gas giant. This discovery was announced in early September 2026, based on observations made as part of Hubble's Outer Planet Atmospheres Legacy (OPAL) program, which annually monitors the solar system's outer worlds.
Scientists Are Watching It Form
Unlike the northern hexagon, which has been a stable fixture for over 40 years, the southern decagon is a work in progress. Astronomers believe it has only recently formed, giving them an unprecedented opportunity to watch a colossal planetary weather system develop in real time. By analyzing archival Hubble data, researchers traced the first faint hints of the structure to images from 2023. Observations in 2024 and 2025 showed the pattern becoming much more distinct. This is especially noteworthy because NASA's Cassini spacecraft, which orbited Saturn from 2004 to 2017, never detected any sign of such a long-lived formation at the south pole, confirming the decagon's recent arrival.
It's Not a Copy of the Northern Hexagon
While it's tempting to call this a simple southern twin to the northern hexagon, the two features are distinctly different. The most obvious distinction is the number of sides: ten in the south versus six in the north. Furthermore, the northern hexagon is famously stable and nearly stationary. In contrast, the southern decagon appears more dynamic and is still evolving. Its vertices, or corners, vary in sharpness, suggesting the structure is not yet settled. This has led scientists to speculate that the decagon might be a different kind of atmospheric wave, one that formed through a separate process than its northern cousin.
A Deep, Multi-Layered Structure
This isn't just a pattern painted on the cloud tops. Hubble's observations, taken at different wavelengths of light, reveal that the decagon is a deep, vertically extended structure that persists through multiple layers of Saturn's atmosphere. This tells scientists that the wave is a significant atmospheric phenomenon, not just a superficial feature. It is deeply rooted in the jet stream, a band of wind raging hundreds of miles per hour. Understanding how such a structure can maintain its shape across different atmospheric layers is a key question that researchers hope to answer with future observations from both Hubble and the James Webb Space Telescope.
Timing Was Everything, Thanks to Seasons
The discovery was made possible by Saturn's long and tilted seasons. Like Earth, Saturn has an axial tilt, meaning its poles nod towards and away from the Sun over its 29-year orbit. For years, from 2012 until 2023, the planet's south pole was tilted away from Earth, hiding it from view. As Saturn's southern spring arrived, the pole came back into view, allowing astronomers—including a network of amateur observers—to spot a strange, undulating band in 2024. Hubble's powerful and sharp vision then confirmed the 10-sided nature of the feature, turning a faint hint into a landmark discovery. It was a perfect case of being in the right place at the right time to see Saturn unveil a new secret.
