A Bizarre Ten-Sided "Decagon" Jet Turns Up Over Saturn's South Pole

Scientists have spotted a bizarre polygon surrounding Saturn's south pole, a feature that has puzzled them because it was not seen earlier despite years of close study. Saturn's north pole has had a hexagonal, cloud-darkening jet of gas for at least 45 years, first spotted when NASA's Voyager probes flew past the planet in 1980 and 1981. NASA's Cassini mission studied Saturn for more than 13 years but never observed anything similar in the southern hemisphere.

Using the Hubble Space Telescope and the help of a network of amateur astronomers, researchers have now identified a similar 10-sided jet moving independently of the rest of the atmosphere around Saturn's south pole, according to a study published September 2 in the journal Science Advances. The decagon first became apparent in Hubble images gathered last autumn; astronomers then revisited observations from as early as 2023 and confirmed it was visible then too, although less defined. Because no spacecraft has been stationed at Saturn since 2017, and the planet's south pole was turned away from Earth from 2012 until it reappeared in 2023, scientists cannot say exactly when the decagon first formed.

"This discovery suggests that the hexagon [at the north pole] is not as extraordinary as previously thought," said planetary scientist Agustín Sánchez-Lavega of the University of the Basque Country in Bilbao, Spain. Seeing a jet on Saturn is not unusual on its own, according to MIT planetary scientist Wanying Kang, who was not involved in the research: the planet's large size and fast spin, with a day lasting only about 10.7 hours, naturally whips gas flowing from the warmer equator toward the cooler poles into stripy bands circling the planet. But the decagon's angular shape, rather than a smooth circle, is striking, Kang said, and suggests there is something new to learn about Saturn's deeper atmosphere.

The decagon appears to change more than the long-studied hexagon does, said planetary scientist Amy Simon of NASA's Goddard Space Flight Center, which makes her hesitant to predict how long the feature will last. The researchers cannot fully explain the decagon, though they suggest that perturbations from a nearby storm might have triggered it. They hope that recruiting additional observatories, including the James Webb Space Telescope, will help reveal what is creating it; Hubble was already scheduled to observe Saturn again later this month.