A Mysterious Decagon Unexpectedly Appeared Around Saturn's South Pole. The Ten-Sided Shape Seems to Be a Wave in the Atmosphere

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 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. 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. 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.