Scientists Identify Decagonal Storm at Saturn's South Pole, Potential Twin to Long-Standing Hexagon
Hubble observations between 2023 and 2025 revealed a ten-sided atmospheric wave near Saturn's south pole, a structure that appears to be developing unlike the stable hexagonal vortex at the north pole.
Images from the Hubble Space Telescope have captured a growing ten-sided wave around Saturn’s south pole, a feature that first became visible in 2023 as the planet’s tilted axis allowed the southern hemisphere to be observed again. The decagonal pattern, which reached a fully defined shape by August 2024, is thought to have formed between 2023 and 2025 and continues to evolve, according to a study published in Science Advances.
The north-pole hexagon, first identified in Voyager data from 1980 and later imaged in detail by Cassini, is a stable six-sided vortex spanning roughly 30,000 kilometers and persisting for more than four decades. In contrast, the southern decagon’s vertices shift over a roughly 32-day cycle, suggesting it is a meandering atmospheric wave rather than a rigid structure.
"These properties in the movement of the decagon indicate the existence of a complex dynamical behavior, never observed in the hexagon, becoming a subject that deserves future attention," the paper’s authors wrote.
Computer simulations using shallow-water models indicate the decagon could arise from repeated disturbances along the peak of a sub-polar jet or from a large counter-clockwise vortex situated to its north. If so, the decagon may be a transient phenomenon, whereas the hexagon remains a robust, long-lasting wave despite surrounding storm activity. The discovery offers new insight into the formation and evolution of planetary storms.