Hubble Confirms Decagon Around Saturn's South Pole
A new study in Science Advances describes a giant ten-sided atmospheric wave circling Saturn's south pole, discovered through years of observations by the Hubble Space Telescope.
The Hubble Space Telescope has confirmed a ten-sided atmospheric wave structure circling Saturn’s south pole, NASA announced. The discovery was published on September 2, 2026, in the journal Science Advances, in a paper titled “A decagon wave around Saturn’s south pole,” volume 12, issue 36, catalogued as 10.1126/sciadv.aee4251. The lead author is Agustin Sanchez-Lavega, a researcher at the University of the Basque Country in Bilbao.
The structure, which scientists named the decagon, sits inside one of Saturn’s powerful jet streams and resembles, in shape, the planet’s well known northern hexagon. That hexagon has been documented since the Voyager 1 and Voyager 2 flybys of 1980 and 1981 and has since been described as remarkably stable. The southern decagon, according to the study, behaves differently: rather than staying fixed, it is intensifying. NASA places the structure at roughly 63 degrees south latitude, while the outlet Nova reports a slightly broader band, from 60 to 63 degrees.
The discovery became possible because Saturn’s south pole, owing to the planet’s axial tilt and the changing seasons, has gradually swung back into view for observers on Earth. The observations are part of the OPAL program (Outer Planet Atmospheres Legacy), which has photographed the outer planets of the solar system every year for more than a decade. Its principal investigator is Amy Simon of NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
How the structure was spotted
The first hint of a ten-sided shape appeared in Hubble images taken through a red filter in October 2023, though it was not clearly defined at the time. By August 2024 the shape had sharpened noticeably, spotted by Sanchez-Lavega along with amateur astronomers Trevor Barry and Jean-Paul Auger, who were analyzing images taken from Earth. During August and September 2025, all ten vertices of the structure were fully formed, although the brightness of individual vertices varied unevenly around the shape.
The structure extends through multiple layers of Saturn’s atmosphere, which, according to NASA, means it is not merely a cloud-level pattern but a vertically developed atmospheric phenomenon. The wavelength between its characteristic segments measures about 16,782 kilometers, more than the diameter of Earth.
Amy Simon described the discovery this way: “We’ve never seen anything like this on Saturn’s southern hemisphere.” She added:
“This feature is different, it appears to be intensifying, giving us a rare opportunity to watch a huge atmospheric pattern evolve.”
That observation, according to NASA’s statement, is also the biggest contrast with the northern hexagon, which has stayed essentially unchanged in every available image since the Hubble team began looking for it in 1990, including images from the Cassini spacecraft, which orbited Saturn between 2004 and 2017 and never recorded a decagon.
What the study does not prove
The study’s authors stress that understanding what causes the decagon will require further observation, both from Hubble and from the James Webb Space Telescope, along with computer modeling. The paper does not establish the mechanism behind the structure, does not explain why it appeared now, after more than three decades of searching, and does not answer whether the decagon will stabilize the way the northern hexagon did or break apart as Saturn’s seasons change.
The data also do not prove a direct causal link to a nearby atmospheric vortex close to the pole, which the researchers mention as a possible but so far unconfirmed factor. NASA says answers to those questions will have to wait for future observing campaigns under the OPAL program.
