Saturn’s north pole captured by Cassini in 2013. (Credit: NASA/JPL-Caltech/SSI/CICLOPS/Kevin M. Gill)
Although some would argue that the hexagon is the bestagon, astronomers have discovered that Saturn appears to favor the ten-sided decagon on its south pole. This comes as its south pole has recently been confirmed to show a pattern that’s oddly ten-sided, per a recent research article by [Agustín Sánchez-Lavega] et al. in Science Advances.
Because Saturn is a gas giant, this naturally isn’t some gigantic planet-sized rock formation, but rather an interesting wave phenomenon in this massive gas bubble. The hexagon shape on its north pole had been known about for a while already, so it is perhaps not too surprising to find something similar on its south pole.
These shapes are generally the result of standing waves within a polar vortex, through the interaction of waves in Saturn’s atmosphere. For the north pole hexagon, the formation is driven by an intense eastward jet, but no similar wave had been reported for the planet’s south pole.
While in this paper a decagon shape is identified based on multiple observations, they postulate that it’s due to a meandering wave in the area rather than a jet as at the other pole. This clearly doesn’t make this wave pattern as obvious as the one at the north pole, but it provides another fascinating insight into fluid dynamics scaled up to a planetary gas giant.
NASA’s Hubble Tracks New Decagon Encircling Saturn’s South Pole
Recent NASA Hubble Space Telescope images show the gas giant Saturn and its southern pole, where astronomers have discovered a 10-sided atmospheric wave. Observations show the decagon extends through multiple layers of Saturn’s atmosphere.
Image: NASA, ESA, STScI, Agustin Sánchez-Lavega (UPV), Amy Simon (NASA-GSFC), Michael Wong (UC Berkeley); Image Processing: Alyssa Pagan
Recent observations with NASA’s Hubble Space Telescope have revealed a giant, evolving, 10-sided atmospheric wave encircling Saturn’s south pole. This discovery marks the first time a large, regular-sided jet pattern has been observed in the planet’s southern hemisphere. The feature appears remarkably similar to Saturn’s famous hexagon at its northern pole, but is also distinctly different, suggesting scientists may be witnessing a new atmospheric phenomenon develop on the iconic gas giant.
The results published Wednesday in the journal Science Advances.
By piecing together several years of Hubble observations dating back to 2023, researchers found subtle hints of the structure beginning to emerge before it became a clearly defined pattern. Those 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 Amy Simon, study co-author and OPAL principal investigator, NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “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.”
The discovery was possible because Saturn’s changing seasons gradually brought the planet’s south pole back into view from Earth, where astronomers who collectively analyze images of Saturn from ground-based observatories first identified it.
Agustín Sánchez-Lavega, lead author of the new study, is a researcher at the University of the Basque Country in Spain. The university manages a website, called Planetary Virtual Observatory Laboratory, that accepts ground-based images of solar system planets contributed by observers all over the world. It was in those images, first in 2024, that Sánchez-Lavega and amateur astronomers Trevor Barry and Jean-Paul Oger noticed a subtle undulating band along the southern pole. Additional 2025 imagery taken from the ground hinted even more strongly toward this decagon structure.
That’s when the Hubble observations come into the picture. Hubble’s view from space offers unmatched image sharpness and spatial resolution over full rotations of Saturn, without smearing by Earth’s atmosphere.
“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. “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.”
A single filter from NASA’s Hubble Space Telescope distinctly shows a 10-sided wave encircling Saturn’s south pole, labeled “decagon”. An “X” denotes where data was not captured.
Image: NASA, ESA, STScI, Agustin Sánchez-Lavega (UPV), Amy Simon (NASA-GSFC), Michael Wong (UC Berkeley); Image Processing: Alyssa Pagan
The 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 decagon’s apparent position shifts slightly, because Hubble captures images from different wavelengths. Those different wavelengths probe different altitudes in Saturn’s atmosphere.
“The most intriguing part to me is that this seems to have just formed recently,” said Simon. “The question is, why did it suddenly form now when we haven’t seen one before?”
The authors say further study is needed from Hubble and NASA’s 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.
Hubble’s long duration in operation has allowed astronomers to track changes over time in solar system planets and other astronomical objects as well.
Rather than providing a single snapshot, the OPAL program allows scientists to follow seasonal changes, track short-lived storms, and identify other atmospheric features that evolve slowly over time.
“When we started the OPAL program, we expected compelling surprises, but we didn’t know what to expect specifically,” said Mike Wong, study co-author, University of California, Berkeley. “A lot of the discoveries we see coming from OPAL are not just based on one observation, but on years and years of data. Regular observations over time are enabling a lot of new findings.”
The team plans to continue observing Saturn to determine whether the decagon settles into a long-lived, stable configuration like the northern hexagon or continues to evolve. Future observations also could help scientists determine what drives the wave, what it reveals about the atmospheric dynamics of giant planets throughout the solar system, and how they may relate to those we see here on Earth.
The Hubble Space Telescope has been operating for more than three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.
Recent NASA Hubble Space Telescope images show the gas giant Saturn and its southern pole, where astronomers have discovered a 10-sided atmospheric wave. Observations show the decagon extends through multiple layers of Saturn’s atmosphere.
Decagon on Saturn’s South Pole (Single Filter)
A single filter from NASA’s Hubble Space Telescope distinctly shows a 10-sided wave encircling Saturn’s south pole, labeled “decagon”. An “X” denotes where data was not captured.
Use the Moon to find Antares and the Teapot, spot brilliant Venus, welcome the equinox, and see the Harvest Moon near Saturn and Neptune.
Skywatching Highlights
Sept. 14-20: Use the Moon to find Antares and the Teapot; dark skies may reveal the Milky Way center
Sept 18: Venus reaches peak brilliance for this evening appearance
Sept. 22: September equinox; fall begins in the Northern Hemisphere and spring in the Southern Hemisphere
Sept. 26: Harvest Moon rises near Saturn and Neptune
Birds fly over a barn as a harvest Moon rises.
Mike Linnihan
Transcript
The Moon joins a tea party… Venus cranks up the brightness… the seasons officially change… and the Harvest Moon meets up with some planetary neighbors.
That’s What’s Up for September.
A sky chart looking southwest after sunset on Sept. 20, 2026.
NASA/JPL-Caltech
From September 14 through 20, let the Moon guide you to a few celestial landmarks. About an hour after sunset, look south to find the Moon in the evening sky.
Night by night, the Moon shifts position against the background stars, passing near Antares.
This bright, reddish star marks the heart of the constellation Scorpius.
Next you’ll see the Teapot, a group of stars in neighboring Sagittarius that really does resemble a teapot, complete with a handle, lid, and spout.
If you are under an especially dark sky… you may see hazy steam rising from the Teapot’s spout. Follow that steam to its thickest part, and you’ll be looking toward the center of our Milky Way galaxy.
A sky chart looking west after sunset on Sept. 18, 2026.
NASA/JPL-Caltech
Look west on September 18 as Venus hits peak brilliance, shining at its brightest of this evening appearance..
You won’t have to search hard to find it. Shortly after sunset, Venus will stand out as a brilliant point of light low above the western horizon, outshining every star around it. A clear view of the horizon will give you the best chance to catch it before it sets.
On September 19, celebrate International Observe the Moon Night!
People around the world are invited to look up and connect with our nearest celestial neighbor while learning more about lunar science, exploration, and the many ways the Moon has shaped cultures around the world. Find an event near you — or learn how to participate from wherever you are — at go.nasa.gov/ObserveTheMoon.
Then on September 22, it’s officially fall in the Northern Hemisphere …while spring begins in the Southern Hemisphere.
That’s the September equinox, when the Sun is directly above Earth’s equator and day and night are close to equal in length around the world.
From there, daylight keeps getting shorter in the Northern Hemisphere and longer in the Southern Hemisphere.
A sky chart looking east after sunset on Sept. 26, 2026.
NASA/JPL-Caltech
And on September 26, the Harvest Moon takes center stage, rising in the east shortly after sunset.
It won’t be alone. Saturn appears nearby, with faint Neptune completing a wide triangle in the sky.
Saturn is the easy one-you can see it with just your eyes. Neptune is a bit more challenging. At around magnitude 8, it’s too faint to see with the unaided eye …so you’ll need binoculars or a telescope to spot it. Darker skies and good observing conditions can help bring it into view.
Here are the phases of the Moon for September.
The phases of the Moon for September 2026.
NASA/JPL-Caltech
You can stay up to date on all of NASA’s missions exploring the solar system and beyond at NASA Science. I’m Raquel Villanueva from NASA’s Jet Propulsion Laboratory, and that’s What’s Up this month.
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