Astronomers using the Hubble Space Telescope have found a giant, ten-sided wave of wind wrapping around Saturn’s south pole, a feature that has never been documented there before and appears to be growing stronger the more scientists watch it. The discovery gives researchers a rare chance to observe a large atmospheric pattern take shape on a gas giant in something close to real time, rather than piecing together its history after the fact. Saturn’s north pole has had a similar, far more famous companion for decades, but nothing like it had ever turned up in the south.
A Decagon to Match Saturn’s Northern Hexagon
Saturn’s north pole is ringed by a persistent, six-sided jet stream known as the hexagon, a feature so stable it has shown up in every observation of the pole for more than 40 years. The newly identified southern counterpart is different in shape, with ten sides instead of six, and different in behavior, since it appears to be a much younger and still-evolving structure rather than a fixed fixture of the planet’s atmosphere. “We’ve never seen anything quite like this in Saturn’s southern hemisphere,” said Amy Simon, a co-author of the study and principal investigator of the Hubble program that captured it. “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.”
Why a Jet Stream Would Bend Into a Polygon at All
Scientists studying Saturn’s northern hexagon have generally attributed its straight-sided shape to the behavior of Rossby waves, large undulations that form inside fast-moving jet streams when a planet’s rotation interacts with the atmosphere’s own flow. Under the right conditions, these waves can lock into a stable, standing pattern with a fixed number of sides rather than a smooth circle, similar to the way ripples on a rotating fluid can settle into a repeating geometric shape in laboratory experiments that have reproduced hexagon-like patterns using nothing more than a rotating tank of liquid. A jet stream with more, smaller undulations would be expected to produce a shape with more sides, which is consistent with a ten-sided decagon representing a different balance of wind speed and wave count in the south than the six-sided pattern locked in place at the north.
Amateur Astronomers Spotted It First
Credit for the earliest hint of the decagon goes not to a space telescope but to ground-based observers piecing together images from around the world, according to comments NASA’s Hubble mission team released alongside the new findings. Agustín Sánchez-Lavega, the study’s lead author and a researcher at the University of the Basque Country in Spain, along with amateur astronomers Trevor Barry and Jean-Paul Oger, first noticed a subtle undulating band around Saturn’s south pole in 2024 using images submitted to the university’s Planetary Virtual Observatory Laboratory, an online archive that accepts contributions from observers worldwide. Additional ground-based images gathered in 2025 strengthened the case that the band was organizing into a distinct ten-sided shape, setting the stage for Hubble to confirm it with far sharper, space-based imagery.
Hubble Traces the Pattern Back to 2023
Once researchers knew what to look for, they returned to years of archived Hubble images taken through the telescope’s Outer Planet Atmospheres Legacy program, which has photographed Saturn and the other outer planets annually for more than a decade. That review pushed the decagon’s confirmed presence back to 2023, even though it only became clearly defined in more recent observations. By contrast, NASA’s Cassini spacecraft, which orbited Saturn between 2004 and 2017 and would have had ample opportunity to spot a long-lived feature, saw no sign of it at all, according to Live Science’s report on the findings. “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, underscoring just how long researchers had been looking before finally finding one.
A Structure That Reaches Deep Into the Atmosphere
The decagon is not simply a pattern in the clouds. Observations show the wave extends through multiple layers of Saturn’s atmosphere, sitting within one of the planet’s powerful jet streams rather than floating at a single altitude, evidence that it is a genuine, vertically extended atmospheric structure rather than a surface-level illusion. Because Hubble captures images across different wavelengths of light, and different wavelengths probe different depths of Saturn’s atmosphere, the decagon’s apparent position shifts slightly depending on which filter astronomers use, a detail that helped confirm its three-dimensional nature rather than undermine it.
Why the Timing Is the Real Mystery
What puzzles researchers most is not that the decagon exists, but that it appears to have formed so recently after decades of nothing. “The most intriguing part to me is that this seems to have just formed recently,” Simon said. “The question is, why did it suddenly form now when we haven’t seen one before?” The research team says further observations from Hubble and the James Webb Space Telescope, along with computer modeling, will be needed to figure out how the decagon formed, whether it will settle into a long-lived feature like its northern counterpart or dissipate, and what it might reveal about how jet streams and polar vortices behave on gas giants generally, comparisons that could eventually extend to similar dynamics in Earth’s own atmosphere. The findings were published in the journal Science Advances.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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