Hubble Detects a New Ten-Sided Atmospheric Wave Circling Saturn's South Pole

A paper published on 2 September 2026 in Science Advances reports the first large, regular-sided atmospheric wave ever observed circling Saturn's south pole: a ten-sided pattern, or decagon, sitting inside a fast jet stream near 63°S. The finding, announced the same day by the Space Telescope Science Institute in Baltimore, comes from years of NASA/ESA Hubble Space Telescope imaging, and the authors are explicit that they do not yet have an explanation for why the structure appeared when it did.

What the Hubble data show

The team, led by Agustín Sánchez-Lavega of the University of the Basque Country with co-authors including Amy Simon of NASA's Goddard Space Flight Center and Michael Wong of the University of California, Berkeley, pieced the discovery together from Hubble images collected under the Outer Planet Atmospheres Legacy (OPAL) program, which has photographed Saturn, Jupiter, Uranus and Neptune every year for more than a decade. Faint hints of a wavy band near the south pole appear as far back as 2023. Ground-based observations contributed by amateur astronomers Trevor Barry and Jean-Paul Oger, credited in the ESA/Hubble release accompanying the paper, strengthened the case through 2024 and 2025, and a Hubble image taken on 29 August 2025 shows the pattern as a clearly defined, sharpening decagon.

According to the paper, the wave is not confined to the cloud tops: it extends through multiple layers of Saturn's atmosphere, tracing the path of a jet stream rather than sitting as a surface cloud feature. Saturn's winds at these latitudes have been measured at up to 500 miles per hour (800 km/h), among the fastest sustained winds recorded on any planet in the solar system, according to BBC Sky at Night Magazine's reporting on the release.

A counterpart to the northern hexagon, but not a twin

Saturn's north pole has carried a six-sided jet-stream pattern, the hexagon, since it was first captured in Voyager spacecraft imagery in 1981; NASA notes it has remained stable for more than 40 years. Researchers had been looking for a southern counterpart since at least 1990, per Sánchez-Lavega's comments accompanying the release, given the rough north-south symmetry expected in Saturn's jet system. The decagon is that counterpart in the loose sense that it is a large, closed, straight-sided wave locked to a polar jet — but it has ten sides rather than six, and unlike the long-settled hexagon, it appears to be new and still strengthening.

"We've never seen anything quite like this in Saturn's southern hemisphere," Amy Simon, OPAL's principal investigator, said in the STScI release. "The feature is different — it appears to be strengthening, giving us the rare opportunity to watch a giant atmospheric pattern develop." Sánchez-Lavega framed the open question directly: why did a large geometric wave suddenly form now, when none had been detected in the decades of prior observation.

What remains unresolved

The paper and the accompanying institutional statements are consistent in treating the discovery as an open problem rather than a settled result. The mechanism proposed — that the straight-sided geometry emerges from wave interference where a fast polar jet meets slower-moving air closer to the pole — is described as a candidate explanation, not a confirmed one. Michael Wong is quoted in the release noting that findings like this depend on "years and years of data" rather than a single observation, underscoring that the decagon's long-term stability, unlike the hexagon's four-decade record, is still unknown.

The authors say further Hubble monitoring, additional James Webb Space Telescope observations, and atmospheric modeling will be needed to determine how the wave formed and whether it will persist. Hubble was scheduled for follow-up observations of Saturn later in September 2026 specifically to check whether the sharpening trend seen through 2025 has continued.

Why it matters beyond Saturn

Standing waves locked to polar jets are not unique to Saturn — similar behavior shows up in models of fluid dynamics on rotating spheres, including, in modified form, in Earth's own polar vortex research. A second geometric polar wave on the same planet, forming decades after the first was catalogued, gives atmospheric scientists a rare natural experiment: two structurally similar but non-identical features on the same body, observed under different amounts of solar heating at each pole, that can be compared directly using a decade-plus of consistent instrumentation from the same telescope program.