A Mysterious Decagon Unexpectedly Appeared Around Saturn’s South Pole. The Ten-Sided Shape Seems to Be a Wave in the Atmosphere
Decades ago, scientists found a hexagon around Saturn’s north pole. Now, recent images reveal a decagon in the planet’s southern hemisphere—and it seems to have recently formed
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Many people are used to envisioning the universe in terms of rounded shapes: think spherical bodies and elliptical orbits. But the geometry of the cosmos is more complex than that.
In a study published yesterday in Science Advances, researchers describe the discovery of a decagon—a ten-sided polygon—wrapped around Saturn’s south pole. It appears to be a huge, evolving atmospheric wave within one of the planet’s jet streams. Scientists don’t know what caused its sudden appearance, and they’re not sure how long it might stick around.
“The discovery of the wave really did come as a surprise, as neither earlier images of Saturn taken by the Hubble Space Telescope nor those captured by the Cassini spacecraft whilst orbiting the planet between 2004 and 2017 had shown it,” Agustín Sánchez-Lavega, lead author of the study and a planetary scientist at the University of the Basque Country in Spain, tells Science Alert’s Michelle Starr.
The finding emerged with the help of citizen scientists. In 2024, Sánchez-Lavega and two amateur astronomers—Trevor Barry and Jean-Paul Oger—spotted an almost undetectable undulating band in images of the gas giant’s southern pole. The data had been stored in the Planetary Virtual Observatory Laboratory, which accepts ground-based images of solar system planets from around the world.
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More images the following year provided further evidence for a decagon structure, and the matter was ultimately confirmed with observations from the Hubble Space Telescope, per a statement from the European Space Agency. The decagonal wave is thick enough to extend through multiple layers of the atmosphere, suggesting that it’s more than a cloud-level structure.
Scientists realized that Hubble had spotted the decagon as far back as 2023. But they can’t pinpoint exactly when it formed. The planet hasn’t been studied by an orbiting spacecraft since Cassini’s mission ended in 2017, and due to the gas giant’s tilt on its axis, its south pole was turned away from Earth between 2012 and 2023. So, astronomers suspect the structure appeared between 2017 and 2023.
Did you know? Saturn’s tilt
Saturn has an axial tilt of 26.73 degrees, which means the planet experiences seasons, like Earth does. One day on Saturn is just 10.7 hours, but a year on the gas giant is 29.4 Earth years.
Saturn’s large size and fast spin facilitate the formation of jet streams on the ringed planet, as Wanying Kang, a planetary scientist at MIT who did not participate in the study, tells Science News’ Meghan Bartels. What’s notable is that the decagon has an angular shape instead of being a smooth circle. It indicates that scientists might discover something interesting, possibly regarding Saturn’s deeper atmosphere, with additional research, she adds.
While the decagon seems to be a relatively new structure, Saturn’s experience with polygons goes back much further. More than 40 years ago, the two Voyager spacecraft discovered another regular-sided feature on the planet: a hexagonal jet stream around its north pole that’s still around today.
The study demonstrates that “the ‘unique’ hexagon is not as extraordinary as we thought,” Sánchez-Lavega tells the Associated Press’ Marcia Dunn.
Still, there are several differences between the two shapes. “The one at the north is a bit smaller,” Amy Simon, a senior scientist in planetary atmospheres research at NASA and a co-author of the study, tells New Scientist’s Jonathan O’Callaghan. The south pole formation is also apparently growing in strength, she explains in the statement, “giving us the rare opportunity to watch a giant atmospheric pattern develop.”
As for the most obvious difference—the number of sides—“it may be linked to the difference in latitude, to the background wind structure or perhaps even to the presence of a high-pressure vortex at nearby latitudes that could be forcing the formation of the wave,” Sánchez-Lavega tells Science Alert.
As is often the case with scientific mysteries, the answer lies in collecting additional data and conducting further analysis. The research team intends to keep an eye on Saturn to see whether the decagon will continue to transform or ultimately settle, like its northern counterpart seems to have done long ago.
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