Back in the 1980s, Voyager probe images of Saturn revealed a structure unique to the solar system: a huge, amazingly regular hexagon around the gas giant’s north pole. This hexagon consists of a central vortex surrounded by a sharply defined hexagonal flow band. Images from NASA’s Cassini probe and the Hubble Telescope confirm that this Saturn hexagon still exists today – meaning it has been stable for more than 40 years.
Puzzle about Saturn’s south pole
The strange thing, however, was that there seemed to be no such formation at Saturn’s south pole. “Given the symmetry of Saturn’s jet stream system, we have been looking for a counterpart to Saturn’s northern hexagon at the south pole since 1990,” reports Agustín Sánchez-Lavega from the University of the Basque Country in Bilbao. “Images from NASA’s Cassini spacecraft, which orbited Saturn between 2004 and 2017, also provided no evidence of such a formation.” From 2012 to 2023, Saturn’s south pole was not visible from Earth because the planet had its northern half facing us.
Now something surprising is emerging at Saturn’s long-hidden south pole: images from the Hubble Space Telescope and several ground-based telescopes now reveal a regular, angular formation at the south pole of the ringed planet. However, this is not hexagonal like at Saturn’s north pole, but decagonal. “We have never seen anything like this on Saturn before,” says co-author Amy Simon of NASA’s Goddard Space Flight Center.
13,000 kilometer wide corner band
Further analysis shows that Saturn’s newly discovered decagon is formed by ten regularly spaced vortices. Together, they redirect the gas flows of the polar wind bands so that a ten-sided standing wave forms. “Three of the corners and edges are very noticeable, four are slightly less prominent and three are only weakly defined,” report the researchers. The decagonal band is around 13,000 kilometers wide and lies between the planet’s 53rd and 66th parallels south.
This strange decagon shape can be seen in different wavelengths and extends into the deep layers of Saturn. “It is therefore a multi-layered phenomenon, divided into several levels,” report Sánchez-Lavega and his colleagues. In this respect, the South Pole Decagon is similar to the famous hexagon at Saturn’s North Pole.
Hubble images of Saturn’s south pole in two different wavelengths. The decagon can be seen in both. — © NASA/ESA, A. Sánchez-Lavega (University of the Basque Country, EHU)
Why has the Decagon only emerged now?
But there is a crucial difference: “The hexagon at the North Pole has been observed for more than 40 years. But this phenomenon is different,” says Simon. The South Pole decagon appears to have only formed in 2023 and has gradually become more apparent since then. “The question, however, is why it only emerged now – and why we have never seen anything comparable at Saturn’s south pole before,” said the astronomer.
If the south pole decagon depended on the seasons and only appeared in Saturn’s southern summer, it should have been seen earlier. The southern half of Saturn faces the sun for around 15 years before the northern half is more irradiated for 15 years. But in images taken by the Hubble Telescope in the 1990s, no angular formation can be seen at Saturn’s south pole. “Despite decades of observation, a comparable wave structure has not been observed at the South Pole or anywhere else on Saturn,” report the researchers.
Will the decagon remain?
The future of the South Pole decagon is just as mysterious as its creation: whether this decagonal flow structure will soon dissolve again or whether it will have a similar longevity as the North Pole hexagon is currently still completely open. The astronomers therefore want to continue to keep an eye on the phenomenon and also use the James Webb Telescope. This may reveal features that shed more light on the mechanism, exact structure and future of the new decagon at Saturn’s south pole.
Source: Agustín Sánchez-Lavega (Universidad del País Vasco, Bilbao) et al., Science Advances, 2026; doi: 10.1126/sciadv.aee4251