Hubble Finds Ten-Sided Wave Over Saturn's South Pole
Hubble spotted a ten-sided wave in the clouds over Saturn's south pole, the first such pattern ever recorded on that hemisphere, according to a study published September 2 in Science Advances.
NASA says the Hubble Space Telescope has captured a huge, shifting ten-sided wave in the clouds over Saturn’s south pole. It is the first regular, multi-sided structure ever observed on the gas giant’s southern hemisphere. The study describing the find was published on September 2, 2026, in the journal Science Advances, under DOI 10.1126/sciadv.aee4251, with lead author Agustin Sanchez Lavega of the University of the Basque Country in Spain.
The feature is already being compared to Saturn’s better known hexagon over the north pole, first spotted by the Voyager probes back in the 1980s and seen every time a telescope has turned toward that region since, for more than 40 years, longer than a single Saturnian year, which lasts about 30 Earth years. The southern decagon is different: according to the study’s authors, it looks like it is still intensifying.
We’ve never seen anything like this on Saturn’s southern hemisphere. The northern hexagon has been there every time we’ve looked, for more than 40 years. This feature is different, it appears to be growing stronger, giving us a rare chance to watch a major atmospheric pattern as it forms.
That’s Amy Simon, a scientist at NASA’s Goddard center, in a statement from the agency. Simon co-authored the study and leads the agency’s Outer Planet Atmospheres Legacy program, known as OPAL.
Traced Back to 2023
Study co-author Michael Wong of the University of California, Berkeley, helped the team piece together a timeline from several years of Hubble images gathered under OPAL, which has photographed the outer planets once a year for more than a decade. The first faint traces of the structure turned up in 2023 images, while earlier observations showed nothing at all. The researchers believe the decagon formed sometime between 2017 and 2023, while Saturn’s south pole was tilted away from Earth and out of view of the instruments.
From Earth, amateur astronomers Trevor Barry and Jean-Paul Auger were the first to catch a trace of it, spotting a faint wavy band along the south pole in 2024 in images collected through a University of the Basque Country website built specifically for amateur planetary observations. 2025 images further reinforced the picture of a ten-sided structure, and it was Hubble, with its sharpness and its ability to capture a full planetary rotation undisturbed by Earth’s atmosphere, that confirmed the shape.
What I find most interesting is that this appears to have formed only recently. The question is why it suddenly formed now, when we hadn’t seen it before.
Simon added, according to both NASA’s statement and the Phys.org report.
How Big Is the Decagon, and How Long Will It Last?
Sources disagree on the structure’s exact width. The Associated Press, as carried by ClickOnDetroit, states only that one side of the decagon exceeds 16,700 kilometers, or 10,000 miles, without giving a figure for the shape’s overall width. That number would suggest the full decagon, with ten roughly equal sides, could be around 167,820 kilometers across, though the sources do not explicitly confirm that math as an official measurement.
The wave sits inside one of Saturn’s powerful jet streams and, according to the authors, does not stay confined to the ammonia ice cloud layer but extends through multiple layers of the atmosphere, meaning it is vertically developed. It moves eastward at roughly 10 kilometers per hour, or 6 miles per hour, while the northern hexagon is essentially stationary.
This is a very interesting feature that appears to be unique to Saturn, and we want to know why.
Sanchez Lavega told the Associated Press, adding that there may be a link to the polygon-shaped clusters of cyclones seen on Jupiter. Leigh Fletcher of the University of Leicester measured the wind speed inside the decagon using the European Southern Observatory’s Very Large Telescope in Chile.
Saturn can still surprise us.
Fletcher said in a statement to the Associated Press. On the launch of the OPAL program itself, Wong told NASA for its statement:
When we started the OPAL program, we expected interesting surprises, but we didn’t know exactly what to expect. Many of the discoveries coming out of OPAL aren’t based on a single observation but on years and years of data.
This is the first time we have covered either Saturn’s decagon or its hexagon. Among our earlier stories on gases and clouds in space, we reported on a newly found cloud near the center of the Milky Way that contains more than 120 molecules.
Sanchez Lavega also told the Associated Press that, for now, he can go no further than confirming the feature is still there: “For now, I can only confirm that the decagon is still there.” Further observations, both with Hubble and with the James Webb Space Telescope, together with computer modeling, are expected to show how the structure formed, how long it might last, and whether, like the northern hexagon, it will remain stable for decades.
The study itself, based on just three years of Hubble images, proves neither how long the decagon will last nor exactly what is driving its formation. The authors describe that as an open question, not a conclusion.
