Hubble detects ten-sided atmospheric wave at Saturn's south pole

Astronomers analyzing images from the NASA/ESA Hubble Space Telescope have discovered a ten-sided wave, or decagon, surrounding Saturn's south pole. The structure spans roughly 104,000 miles (about 167,800 km) with each side measuring around 10,400 miles (16,800 km). Centered near 63 degrees south latitude, the feature rides a fast eastward jet and appears to be strengthening.

The discovery, reported in a paper published in Science Advances and led by Agustín Sánchez-Lavega of the University of the Basque Country, builds on observations from the Outer Planet Atmospheres Legacy (OPAL) program, which provides yearly calibrated images of the outer planets. Ground-based amateur images from 2024-2025 hinted at the pattern, and archival Hubble data showed a faint version in 2023 that grew more distinct in subsequent years.

"The decagon is a visible expression of a wave locked into a powerful eastward jet stream and extends vertically through multiple atmospheric layers," the researchers explained, noting that its apparent position shifts when observed through different filters that probe varying depths.

The finding mirrors the hexagonal jet discovered at Saturn's north pole by Voyager more than four decades ago, suggesting that polygonal jet structures can form under suitable atmospheric conditions on both hemispheres. Differences in the number of sides imply variations in jet speed, width, and shear between the northern and southern poles.

Scientists note that the decagon's emergence after Saturn's southern pole became visible again—following a period when the pole was hidden from Earth—raises questions about its seasonal nature and longevity. Ongoing Hubble monitoring and future observations with the James Webb Space Telescope are expected to track the feature's evolution and probe its depth, while numerical models will aim to reproduce both the hexagon and decagon within Saturn's atmospheric dynamics.