Saturn decagonal wave observed

A newly identified 10-sided wave around Saturn’s south pole adds a southern counterpart to one of the solar system’s strangest long-lived weather patterns. A paper published September 2 in Science Advances reported that Hubble Space Telescope images from 2025, combined with earlier observations, revealed a decagonal atmospheric wave circling the planet’s south polar region. The feature sits at roughly 58°S to 63°S planetographic latitude and appears tied to a jet near the pole, the paper said. ESA and the Space Telescope Science Institute described it as the first large regular-sided jet pattern observed in Saturn’s southern hemisphere. ### Where is the decagon, exactly? The Science Advances paper placed the wave around Saturn’s south pole rather than directly over it. The authors said the decagon occupies a band between about 58 degrees south and 63 degrees south planetographic latitude, where a high-speed jet outlines the polygonal shape. The paper described it as a wave pattern in the atmosphere, not a solid structure or a ring feature. (science.org) ESA said the wave encircles Saturn’s south pole and is evolving, while STScI said the pattern is newly formed. Those descriptions match the paper’s account that the southern feature differs from Saturn’s much older northern hexagon, which has been observed for decades. ### How did scientists spot it now if Cassini ended in 2017? Hubble observations from 2023 to 2025 were central to the detection. (science.org) New Scientist, citing team members Amy Simon of NASA Goddard Space Flight Center and Agustín Sánchez-Lavega of the University of the Basque Country, reported that the feature was first noticed by amateur astronomers in 2024 and then checked against Hubble images. Simon and colleagues examined observations from 2023 through 2025 as the southern hemisphere became visible again. (esa.int) The Cassini mission remains part of the comparison set because it provided the baseline for Saturn’s polar circulation from 2004 to 2017. The new paper says no similar southern wave had been reported during decades of prior observations, which is why the recent emergence matters to the researchers. ### Is this the same thing as Saturn’s famous north-pole hexagon? Saturn’s north-pole hexagon is the closest known analogue, but the two patterns are not identical. (newscientist.com) The northern feature is a six-sided wave close to the north pole that has persisted since at least the Voyager era and was studied extensively by Cassini and later work in Nature Astronomy. The southern feature has 10 sides, appears newer, and seems to move more with Saturn’s rotation, Simon told New Scientist. (science.org) The Science Advances paper said Saturn’s north polar hexagon is a long-lived, nearly stationary wave coupled to an intense eastward jet. By contrast, the southern decagon was described as an evolving wave in the south polar jet system, with no earlier confirmed counterpart in the southern hemisphere. ### What do researchers think is causing it? Agustín Sánchez-Lavega and co-authors described the feature as a planetary-scale atmospheric wave associated with the jet near Saturn’s south pole. (newscientist.com) New Scientist reported that the team linked it to a large atmospheric wave shaped by wind from a powerful jet stream, while Simon said the underlying fluid dynamics are complex. The paper does not present the decagon as fully explained. (science.org) Simon told New Scientist that the structure was unexpected, and the report said researchers are still working out whether a nearby storm helped trigger it. ESA’s release likewise called it an evolving atmospheric wave rather than a settled or fully understood system. ### Why were Cassini-era comparisons still important? (science.org) Cassini’s 2004-2017 observations gave scientists the long baseline needed to say this is new, not merely newly noticed. Earlier studies established the persistence and structure of Saturn’s north-pole hexagon and mapped the planet’s polar dynamics in detail. That historical record is what lets researchers compare the new southern decagon against known jet behavior and earlier seasons on Saturn. (newscientist.com) The next step is continued monitoring with Hubble and Earth-based observers. ESA and STScI said the southern decagon is evolving, and the Science Advances paper provides the published reference point for tracking whether the 10-sided wave strengthens, shifts or fades in future observations. (esa.int) (nature.com)