Astronomers find a 10-sided atmospheric wave around Saturn’s south pole

Astronomers have identified an immense 10-sided wave in Saturn’s southern atmosphere, showing that the planet’s famous north-polar hexagon is not its only polygon-shaped weather system.

The newly documented decagon lies near 60 degrees south and rides on a powerful eastward jet stream. Hubble Space Telescope images reveal that it was present by 2023, after earlier observations by Hubble and the Cassini spacecraft showed no such structure. It became more clearly defined in images from 2025. Each of its sides extends for more than 16,700 kilometers, while the full pattern takes roughly 800 days to travel around Saturn.

Observations at different wavelengths found traces of the shape at multiple altitudes and latitudes, suggesting a layered atmospheric structure rather than a marking confined to the visible cloud tops. Unlike the northern hexagon, which has remained stable for more than four decades, parts of the decagon appear uneven or blurred, indicating that it may still be evolving.

Researchers do not yet know what created it. Possible explanations include an unstable jet stream, disturbances rising from deeper in the atmosphere or influence from a nearby high-pressure vortex. As Saturn’s southern hemisphere moves toward summer, improving views and increasing sunlight should help scientists watch whether the decagon strengthens, changes shape or breaks apart.