In September 2026, astronomers confirmed the discovery of a striking 10-sided atmospheric feature—a decagon—encircling Saturn’s south pole. Unlike the planet’s famous and long-lived hexagonal jet stream at the north pole, which has been observed for more than four decades, this southern structure appears to be relatively new and still evolving. Hubble Space Telescope images from 2023 through 2025, combined with ground-based observations (including some by amateur astronomers), revealed a clear polygonal wave centered near 58° to 63° south latitude. The pattern sits within a powerful eastward jet stream and spans a vast scale, with each side measuring roughly 16,700–16,800 kilometers—longer than Earth’s diameter—making the overall loop around the pole about 168,000 kilometers in circumference.
The decagon is interpreted as a large-scale meandering atmospheric wave (likely a Rossby-type wave) trapped and shaped by the curvature of the surrounding jet stream, which itself races along at around 116 meters per second (about 420 km/h or 260 mph). Remarkably, the polygonal pattern drifts much more slowly eastward at only about 2.5 meters per second, while its ten vertices oscillate longitudinally with a period of roughly 32 days and amplitudes of several degrees. Multi-wavelength Hubble data show the feature extends through multiple atmospheric layers rather than being confined to a single cloud deck, and it has grown more distinct and sharply defined over the observed years. A nearby large storm may have played a role in its formation, though the precise fluid-dynamics mechanisms remain under study.
This southern decagon provides a valuable counterpart to the northern hexagon and challenges earlier assumptions that such regular polygonal waves were unique to Saturn’s north polar region. Because no spacecraft has orbited Saturn since Cassini’s mission ended in 2017, and because the south pole was poorly visible from Earth for years due to the planet’s axial tilt, the feature’s exact start date is still uncertain. Continued monitoring with Hubble and ground-based telescopes will help determine how long the decagon persists, whether it stabilizes like its northern cousin, and what it reveals about the complex atmospheric dynamics of gas giants.
Astronomers discover mysterious 10-sided cloud structure at Saturn's south pole | Space
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