Hubble is tracking a ten-sided wave tightening around Saturn’s south pole

Saturn’s north pole has worn the same six-sided jet stream, nicknamed the hexagon, since the Voyager spacecraft first spotted it more than 40 years ago. Now NASA’s Hubble Space Telescope has found the planet’s southern hemisphere growing a geometric feature of its own: a ten-sided atmospheric wave, roughly 104,000 miles across, encircling Saturn’s south pole. Scientists say it is the first time a large, regular-sided jet pattern has ever been documented in that hemisphere, and nobody yet knows what triggered it or how long it will last.

A Decagon Nobody Had Seen Before

The discovery, detailed in a paper published in the journal Science Advances, came together by piecing apart several years of Hubble imagery gathered through the telescope’s Outer Planet Atmospheres Legacy program, which has photographed the solar system’s outer planets annually for more than a decade. Amy Simon, the program’s principal investigator at NASA’s Goddard Space Flight Center, said the team has never seen anything like it in Saturn’s southern hemisphere, noting that the northern hexagon has appeared in every observation for more than 40 years while this new feature looks like it is actively strengthening.

Ground-Based Astronomers Spotted It First

The first hints came not from Hubble but from a network of amateur and professional astronomers who feed images of the outer planets into the Planetary Virtual Observatory Laboratory, a site run by the University of the Basque Country in Spain, according to a NASA Science release on the discovery. Agustín Sánchez-Lavega, the study’s lead author and a researcher there, said he and observers Trevor Barry and Jean-Paul Oger noticed a faint, undulating band around Saturn’s south pole in ground-based images beginning in 2024, with additional 2025 imagery strengthening the case for a genuine decagon-shaped structure. Sánchez-Lavega noted that his team had been searching Hubble images for a southern counterpart to the northern hexagon since 1990, and that even NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017, never showed any sign of a long-lived pattern at the south pole.

Hubble Confirms a Wave Reaching Back to 2023

Once researchers turned Hubble’s instruments toward the pole, its space-based vantage point, free of the blurring caused by Earth’s atmosphere, allowed a much sharper look than any ground telescope could manage. That analysis confirmed the feature had already been present in 2023, even before ground observers caught on to it, and traced its gradual strengthening in the years since. The wave sits inside one of Saturn’s powerful eastward jet streams and extends vertically through multiple layers of the atmosphere rather than sitting only at the cloud tops, meaning it is a genuinely three-dimensional structure and not a surface marking or an imaging artifact, according to reporting on the same findings.

Each side of the decagon runs roughly 10,000 miles long, and the whole structure is centered near 63 degrees south latitude, placing it well within the region Cassini imaged extensively during its thirteen years orbiting Saturn without ever showing a comparable pattern. That absence in the Cassini record is part of why researchers are treating the decagon as a genuinely new development rather than a long-standing feature that earlier missions simply failed to notice, since Cassini’s cameras were more than capable of resolving a structure of this size had it existed during its mission.

Similar to the Hexagon, but Not Identical

The decagon’s apparent position shifts slightly depending on which wavelength of light Hubble uses to observe it, since different wavelengths reveal different altitudes within Saturn’s atmosphere. That behavior, combined with its ten-sided rather than six-sided geometry, tells researchers the new feature is related to the northern hexagon in the broad sense that both are standing atmospheric waves locked into a jet stream, but is not a simple mirror image of it. Simon called the timing the most intriguing part of the discovery, asking why a pattern like this would suddenly appear now when four decades of observations turned up nothing comparable in the south before.

What Happens Next for Saturn’s New Feature

Researchers say they need more observations, both from Hubble and from the James Webb Space Telescope, along with additional computer modeling, before they can explain how the decagon formed, predict how long it might persist, or determine how closely it will end up resembling its northern counterpart. Mike Wong, a study co-author at the University of California, Berkeley, said the finding underscores the value of the Outer Planet Atmospheres Legacy program’s long-running approach, since discoveries like this one tend to emerge from years of accumulated data rather than any single observation. The team plans to keep watching the pole to see whether the wave settles into a stable, long-lived shape or continues to evolve into something else entirely.

Part of what makes the timing notable is that Saturn’s seasons move slowly, with each one lasting roughly seven Earth years because a full orbit around the sun takes the planet about 29 years. The changing angle of sunlight reaching the southern hemisphere as Saturn’s seasons shift is what first allowed the pole to come back into view from Earth after years spent tilted away, giving both ground-based observers and Hubble a fresh look at a region that had been effectively unobservable for a stretch of the planet’s orbit. Researchers say that seasonal timing alone does not explain why a decagon rather than some other shape emerged, leaving the underlying atmospheric mechanism as the central open question going forward.

This article was created with the assistance of AI and reviewed by an editor.

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