Astronomers have found a giant 10-sided wave encircling Saturn's south pole, and the strangest part is not that a shape with straight edges exists on a ball of gas. It is that this one appears to be forming now, becoming more sharply defined year over year in a matched series of images, which is an unusual thing to catch in progress on another planet.

NASA announced the finding on September 2, drawn from Hubble Space Telescope observations and published in the journal Science Advances. It is the first time a large, regular-sided jet pattern has been observed in Saturn's southern hemisphere. The structure resembles the famous hexagon at its northern pole, which has been studied since 1980, but the team says it is distinctly different, and that scientists may be watching a new atmospheric phenomenon take shape.

"We've never seen anything quite like this in Saturn's southern hemisphere," said Amy Simon, a study co-author at NASA's Goddard Space Flight Center in Greenbelt, Maryland, and principal investigator of the Hubble program that captured the images. Simon noted that the northern hexagon has been present every time astronomers have looked for more than 40 years, while this feature appears to be strengthening.

Amateur Images Pointed Hubble at the South Pole

The trail to the discovery started from the ground. Agustin Sanchez-Lavega of the University of the Basque Country in Spain, the study's lead author, and amateur astronomers Trevor Barry and Jean-Paul Oger noticed a subtle undulating band along Saturn's southern pole in images submitted to the university's Planetary Virtual Observatory Laboratory, a site that collects planetary images contributed by observers worldwide. That was in 2024. Ground-based imagery the following year hinted more strongly at a 10-sided structure.

Hubble settled it. Observing from above Earth's atmosphere, the telescope delivers sharpness and spatial resolution that ground-based instruments cannot match across full rotations of the planet. Researchers pieced together several years of Hubble observations going back to 2023 and found subtle hints of the structure emerging before it became a clearly defined pattern.

Sanchez-Lavega said the team had been searching Hubble images for a southern counterpart to the northern hexagon since 1990, given the symmetry of Saturn's north and south jet stream systems, and that images from NASA's Cassini spacecraft, which orbited Saturn from 2004 to 2017, showed no inkling of a long-lived formation either. The Hubble data confirmed the feature's presence back to 2023.

There is a simple reason nobody caught this earlier. Saturn's changing seasons gradually turned the south pole away from the view from Earth and have only recently brought it back, and no spacecraft has been in orbit at Saturn since the Cassini mission ended in 2017.

A Wave That Runs Deep Through the Atmosphere

The decagon is not a surface marking or a cloud pattern floating alone at one altitude. It sits within one of Saturn's powerful jet streams and extends through multiple layers of the atmosphere, which tells researchers it is a vertically extended structure rather than a shallow cloud feature.

The evidence for that comes from how the pattern behaves across different filters. Hubble images the planet at several wavelengths, and each wavelength probes a different altitude in Saturn's atmosphere. The decagon's apparent position shifts slightly depending on which wavelength is used, and the pattern remains visible across them.

That vertical extent is part of what makes the feature scientifically interesting rather than merely photogenic. Watching a large atmospheric pattern on a giant planet organize itself, rather than studying one that was already fully formed when instruments first arrived, is what Simon described as a rare opportunity.

Differences from the Northern Hexagon

The comparison to the North Pole is the natural one, and also where the caution belongs. The northern hexagon has been observed for more than four decades and has persisted through decades of changing seasons. The southern decagon has been tracked for only a few years, has 10 sides rather than six, and appears to be intensifying rather than holding steady.

Those differences are exactly why the finding has not settled anything. The authors say further study is needed from Hubble and the James Webb Space Telescope, along with 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. Whether it becomes a permanent feature or fades within a few years is an open question the observations cannot yet answer.

The most direct framing came from Simon, who said the intriguing part is that the structure appears to have just formed recently, and that the question is why it suddenly formed now when nothing like it had been seen before.

Observations Planned to Test Whether It Lasts

The images come from Hubble's Outer Planet Atmospheres Legacy program, which has photographed the outer planets annually for more than a decade. Study co-author Mike Wong of the University of California, Berkeley, said many of the discoveries coming from the program rest not on a single observation but on years of data, and that regular observations over time are enabling a lot of new findings.

That design is what makes the next step straightforward. The team plans to keep observing Saturn to determine whether the decagon settles into a long-lived, stable configuration like the northern hexagon or continues to evolve. Future observations could also help identify what drives the wave, what it reveals about the atmospheric dynamics of giant planets generally, and how those dynamics may relate to circulation patterns seen on Earth.

For readers, there is no hazard, no forecast, and nothing to prepare for. The value is different. Saturn is a laboratory for atmospheric physics at a scale no terrestrial experiment can reproduce, and studying how a planetary jet stream organizes itself into straight sides feeds back into the broader physics of polar jets. The full-resolution Hubble images are publicly available, and a companion release from ESA and Hubble is posted in Europe.

What to watch next is the follow-up observing campaign and any modeling results that offer a mechanism. Until then, the accurate statement is narrow and worth keeping straight: a 10-sided wave has been confirmed in Hubble data going back to 2023; it appears to be growing more defined, and no one has yet explained why it started.

What Readers Want to Know

What did astronomers actually find?

A 10-sided atmospheric wave, called a decagon, encircling Saturn's south pole within one of the planet's jet streams. It is the first large regular-sided jet pattern observed in Saturn's southern hemisphere.

How is it different from Saturn's hexagon?

The northern hexagon has six sides and has been present in every observation for more than 40 years. The southern decagon has 10 sides, has been confirmed only back to 2023, and appears to be strengthening rather than holding steady.

Why was it not spotted earlier?

Saturn's seasons had turned the south pole away from the view from Earth, and no spacecraft has orbited Saturn since Cassini ended in 2017. Cassini images showed no inkling of a long-lived formation.

Who found it first?

Ground-based images, including contributions from amateur astronomers, showed an undulating band along the southern pole in 2024. Hubble observations then confirmed the structure and traced it back to 2023.

Is this settled science?

The detection is published in a peer-reviewed journal. The cause is not established. Researchers say further Hubble and Webb observations and computer modeling are needed to explain how it formed and whether it will last.

Does this tell us anything about Earth?

Not directly. The research team says future work could help clarify how giant planet atmospheric dynamics relate to circulation patterns seen on Earth, but no such link has been demonstrated.

Where can the images be viewed?

NASA and the Space Telescope Science Institute have published the full-resolution images and technical captions, and a companion release is available from ESA and Hubble.