For almost five decades, Saturn’s north pole has been famous for hosting a bizarre, six-sided jet stream known as the hexagon, a feature first spotted by NASA’s Voyager spacecraft in the 1980s and still churning today. Astronomers had long wondered whether the ringed planet’s southern hemisphere might hide a mirror-image structure. Now, it turns out the south pole has been quietly growing something of its own: a decagon.
These Hubble images show Saturn and the gas giant’s southern pole with its 10-sided atmospheric wave. Image credit: NASA / ESA / STScI / Agustin Sánchez-Lavega, UPV / Amy Simon, NASA’s Goddard Space Flight Center / Michael Wong, UC Berkeley / Alyssa Pagan.
Saturn’s southern hemisphere dropped out of view from Earth in 2012 because of the planet’s axial tilt, and didn’t become observable again until 2023.
When the images captured by the NASA/ESA Hubble Space Telescope in October 2023 were examined, they showed a faint 10-vertex polygon near 63°S.
By August 2024, the shape had sharpened, and by August-September 2025, Hubble and ground-based observers captured all 10 vertices fully formed, though their brightness contrast varied unevenly around the circle.
The observations were taken as part of Hubble’s Outer Planet Atmospheres Legacy (OPAL) program, which has photographed the outer planets annually for more than a decade.
“We’ve never seen anything quite like this in Saturn’s southern hemisphere,” said OPAL principal investigator Dr. Amy Simon, an astronomer at NASA’s Goddard Space Flight Center.
“The northern hexagon has been there every time we’ve looked for more than 40 years.”
“This feature is different — it appears to be strengthening, giving us the rare opportunity to watch a giant atmospheric pattern develop.”
“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,” said Dr. Agustín Sánchez-Lavega, an astronomer at the University of the Basque Country.
“Images from NASA’s Cassini spacecraft, which orbited Saturn between 2004 and 2017, showed no inkling of a long-lived formation, either. The Hubble data confirmed the feature’s presence back to 2023.”
The decagonal wave sits within one of Saturn’s powerful jet streams and extends through multiple layers of the atmosphere, indicating it is not just a cloud-level feature, but a vertically extended atmospheric structure.
“The most intriguing part to me is that this seems to have just formed recently,” Dr. Simon said.
“The question is, why did it suddenly form now when we haven’t seen one before?”
“Further study is needed from Hubble and the NASA/ESA/CSA James Webb Space Telescope, as well as analysis of computer models, to understand how the decagon formed, how long it may last, and how it compares to the long-lived hexagon in the north.”
A paper about the discovery was published today in the journal Science Advances.
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Agustín Sánchez-Lavega et al. 2026. A decagon wave around Saturn’s south pole. Science Advances 12 (36); doi: 10.1126/sciadv.aee4251
