When NASA’s Voyager spacecraft flew by Saturn in 1980, it detected something unlike anything scientists had seen before: a colossal six-sided storm swirling around the planet’s north pole. The strange hexagon has persisted for decades, becoming one of Saturn’s most mysterious features. But now, astronomers may have found something even more surprising: a similar pattern emerging on the opposite side of the planet. Images captured by the Hubble Space Telescope revealed a growing decagon-shaped wave around Saturn’s south pole. The 10-sided storm appears to have developed between 2023 and 2025 and may be evolving toward this today, unlike its counterpart which has remained stable for more than 40 years. The new discovery is detailed in a paper published Wednesday in Science Advances. A storm is brewing Saturn’s hexagonal storm is one of the gas giant’s most captivating features. Scientists first observed the six-sided vortex in 1988 when they reviewed data from Voyager’s Saturn flyby. The spacecraft’s trajectories prevented them from capturing the entire hexagon, which is twice as wide as Earth. It wasn’t until years later, when the Cassini spacecraft reached Saturn, that scientists were able to observe the enormous storm in all its glory. The storm is about 20,000 to 25,000 miles (30,000 to 32,000 kilometers) wide, with jet streams extending about 180 to 200 miles (300 km) above the cloud tops. A view of Saturn’s hexagonal polar jet stream. Credit: Credit: NASA/JPL-Caltech/Space Science Institute Because of its long-term stability, scientists expected to find a similar wave that had formed in one of two subpolar jets in Saturn’s southern hemisphere. Despite decades of searching, no other waves were detected at the planet’s south pole or anywhere else. Due to Saturn’s tilted axis, its south pole was not visible from Earth as of 2012. It was not until 2023 that scientists were able to see the planet’s southern hemisphere. In October of that same year, Hubble images revealed for the first time a 10-sided polygonal structure at Saturn’s south pole. As the southern hemisphere became more visible, the shape of the decagon became more visible in August 2024. A year later, Hubble images showed all 10 corners of the decagon fully developed. According to the study, three sides of the decagon were very prominent, four were less prominent, and the remaining three were less defined. Twin storm Observations suggest that the decagonal storm developed recently and continues to grow. Unlike its northern hemisphere counterpart, the lengths of the decagon’s vertices change back and forth during a cycle of approximately 32 days. Its movement suggests that the strange 10-sided shape may not be a rigid structure at all, but rather a meandering atmospheric wave, held in place by the curved path of a powerful jet. “These properties in the motion of the decagon indicate the existence of a complex dynamic behavior, never observed in the hexagon, becoming a topic that deserves future attention,” the authors wrote in the article. To better understand how the decagon formed, the researchers used shallow-water model simulations to recreate its behavior. Their results suggest that the shape could have arisen from a repeated perturbation along the peak of the jet, or perhaps been driven by a large vortex rotating counterclockwise to its north. If that’s the case, the decagon could be a transient, evolving phenomenon, while the hexagon is a robust wave that has remained stable for decades despite nearby storm activity. The new discovery provides new information about how storms form and evolve on different worlds and adds more intrigue to a 40-year-old mystery that has persisted on Saturn.
