Hubble found a ten-sided river of wind circling Saturn’s south pole

NASA’s Hubble Space Telescope has revealed a giant ten-sided atmospheric wave around Saturn’s south pole. The shape, called a decagon, is a pattern in the planet’s moving atmosphere rather than a solid structure: a regular-looking boundary made by a jet stream and the cloud layers it organizes.

The discovery is notable because Saturn’s north pole has long been famous for a six-sided jet pattern. The south pole had no known counterpart of that kind. Hubble’s newer observations suggest that the southern feature is developing in real time, giving scientists a chance to watch a large planetary weather pattern emerge rather than merely inspect a long-established one.

A decagon is a wave riding inside Saturn’s atmosphere

NASA’s Hubble report describes a ten-sided atmospheric wave encircling the south pole. The agency says it extends through multiple layers of the atmosphere, which is why it is more than a cloud shape seen in one image. Different Hubble wavelengths probe different altitudes, and the apparent position of the pattern shifts slightly between those views.

Saturn has no solid surface marking out a geometric track. Its visible bands are gas moving at different speeds and directions. A stable-looking polygon can form when a fast jet stream interacts with slower-moving gas closer to a pole. NASA’s Astronomy Picture of the Day explanation says the geometric boundaries may be caused by waves at that boundary between faster and slower flow.

The word “river” is useful as an image of organized motion, not as a literal description. The feature is a circulating atmospheric pattern on a gas giant. It holds a recognizably ten-sided outline in observations while its component gases continue to move, much as a standing wave can retain a shape even though the material involved is in motion.

Hubble’s long view made the new pattern visible

Researchers assembled observations dating back to 2023 and found subtler early signs before the decagon became clearly defined. Those images come from Hubble’s Outer Planet Atmospheres Legacy program, which has photographed the outer planets regularly for more than a decade. Repeated observations matter because a single image can show an unusual cloud boundary without showing whether it persists or evolves.

Agustín Sánchez-Lavega of the University of the Basque Country, the study’s lead author, said the Hubble record confirmed the feature back to 2023. Amy Simon, the OPAL principal investigator at NASA’s Goddard Space Flight Center, said the team had never seen anything like it in Saturn’s southern hemisphere. Their observations were published in Science Advances, according to the NASA account.

Saturn’s changing seasons also made the work possible. The planet takes roughly 29 Earth years to orbit the Sun, and its tilt changes which pole is easiest to see from Earth. NASA’s Saturn fact page notes that the north-pole hexagon spans about 20,000 miles and has been observed for decades; the emerging southern decagon has a much shorter observed history.

The northern hexagon is a comparison, not a template

It is tempting to treat the south-pole decagon as simply the hexagon with four extra sides. NASA stresses the differences. The northern hexagon has appeared whenever scientists have looked for more than 40 years, while the southern pattern appears to be strengthening. Cassini, which orbited Saturn from 2004 to 2017, showed no sign of a long-lived southern formation.

That history gives the new observation scientific value. A large atmospheric pattern that is still developing can help researchers test ideas about jet streams, seasonal sunlight and vertical structure in a way a mature, persistent pattern cannot. The Hubble news archive records the discovery as part of a continuing series of planetary observations, not as a finished explanation of why the shape exists. NASA’s Saturn science collection places the observation within the broader study of the planet’s changing atmosphere.

Hubble has found a ten-sided wind pattern circling Saturn’s south pole. The image is visually remarkable, but the more important point is temporal: observations show a feature taking shape across years and atmospheric layers. Whether the decagon becomes as durable as the northern hexagon remains an open question, and that uncertainty is precisely why continued observation is useful.

Future observations can test whether the boundary sharpens, migrates, breaks apart or settles into a stable pattern. Ground-based observers helped identify the early undulations, while Hubble supplied the full-rotation sharpness that makes the structure easier to measure. That combination is a reminder that planetary science often advances through patient comparison: images that look decorative at first can become a record of atmosphere, season and motion when scientists return to the same world year after year.

The discovery also gives researchers a rare north-south comparison on the same planet. NASA’s Hubble news collection places the observation within a continuing program of space-telescope science. Saturn’s hexagon and decagon share the broad fact of an organized polar jet, yet their histories are different enough to challenge any easy explanation. The more the southern pattern changes, the more useful it becomes for testing which ingredients—wind speed, vertical layers, seasonal energy or polar geometry—make a planetary atmosphere draw a shape that looks engineered.

This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.