Hubble spots mysterious 10-sided ‘decagon’ swirling around Saturn’s south pole —‬ and it wasn’t there a decade ago

New Hubble observations have revealed a dramatic, 10-sided jet surrounding Saturn’s south pole, and it appears to be evolving before our eyes.

The Hubble Space Telescope recently snapped a high-resolution view of the striking “atmospheric wave,” which appears to have begun forming in 2023, archival Hubble images show. Scientists are curious about how this “decagon” popped up so quickly, given that Saturn’s other famous multisided wave — a hexagon at the north pole — has been observed on the planet for 40-plus years.

“The question is, why did it suddenly form now when we haven’t seen one before?” Amy Simon, a senior scientist at NASA’s Goddard Space Flight Center and co-author of a new study describing the observations, said in a statement.

“The northern hexagon has been there every time we’ve looked for more than 40 years,” Simon added. “This feature is different — it appears to be strengthening, giving us the rare opportunity to watch a giant atmospheric pattern develop.”

Scientists can see the wave persisting through several atmospheric layers, which means it extends beyond the cloud tops. The wave is also found in a large jet stream at Saturn. More observations with Hubble and the James Webb Space Telescope (JWST) will be required to see how the wave is generated and what the decagon illustrates about atmospheres in large gas giants like Saturn.

The images were obtained as part of Hubble’s Outer Planet Atmospheres Legacy program, which uses some of the telescope’s time to image the solar system’s outer planets — Jupiter, Saturn, Uranus and Neptune — once a year. The goal is to obtain long-term observations of these worlds, to supplement spacecraft orbiting or flying by.

From Earth’s perspective, Saturn is slowly orbiting in its roughly 29-year journey of the sun so that its south pole is visible from our planet, allowing for a good view of the changing decagon. Hubble, in fact, was not the first to see signs of this decagonal shape; it was ground-based observatories that spotted a mysterious undulating band around Saturn’s south pole in 2024.

Agustín Sánchez-Lavega, first author of the study and a researcher in the Department of Applied Physics at the University of the Basque Country, and amateur astronomers Trevor Barry and Jean-Paul Oger first spotted the forming wave. The trio used the university’s Planetary Virtual Observatory Laboratory, which brings in observations from around the world, to make the Saturnian discovery.

While more images in 2025 showed the wave starting to move into a decagon structure, Hubble was able to obtain high-resolution images without Earth’s atmosphere in the way.

The Cassini spacecraft, which orbited Saturn between 2004 and 2017, didn’t see the feature, hinting that it hadn’t started forming yet, according to NASA. “Given Saturn’s symmetry in its north-south jet stream system, we have been searching for a counterpart to Saturn’s northern hexagon on the south pole in Hubble images since 1990,” Sánchez-Lavega said.

Both Hubble and JWST are expected to provide more opportunities to look at the ringed planet’s developing decagon in the near future. In the meantime, Saturn isn’t the only solar system planet with perplexing polar features; 2017 images from NASA’s Juno spacecraft showed that Jupiter’s south pole is studded with gigantic, oval-shaped cyclones that echo the chaos of the planet’s famous Great Red Spot.