Astronomers have discovered an unusual giant decagonal structure in Saturn’s atmosphere. It surrounds the planet’s south pole and represents a large-scale atmospheric wave associated with a powerful jet stream. The discovery particularly surprised researchers because, until now, Saturn was known for another geometric atmospheric formation — the famous hexagon at its north pole.

The new structure was confirmed thanks to observations by the Hubble Space Telescope. Scientists combined data obtained through the Outer Planet Atmospheres Legacy (OPAL) program, which has been regularly monitoring changes in the atmospheres of the Solar System’s giant planets for more than a decade.

The analysis showed that the first signs of the decagonal wave were already present in Hubble images from 2023, after which it became increasingly pronounced. However, the first clues did not come only from professional observatories. In 2024, the study’s lead researcher, Agustín Sánchez-Lavega of the University of the Basque Country, together with amateur astronomers Trevor Barry and Jean-Paul Oger, noticed an unusual wavy band near Saturn’s south pole in ground-based images.

Observations in 2025 made the geometric shape even more apparent, after which the researchers turned to more detailed Hubble data.

Previously, detecting such a formation was particularly difficult because of the changing seasons on Saturn. The planet’s axial tilt causes its polar regions to periodically become difficult to observe from Earth.

Saturn’s south pole had been facing away from Earth-based observers for a long time, and by the time it became accessible again for detailed observations, the new structure was already present.

Scientists suggest that the decagon may have formed sometime between 2017 and 2023.