A 104,000-mile-wide decagon has formed at Saturn’s south pole, marking the first observed polygonal storm in the planet’s southern hemisphere and offering new insights into atmospheric dynamics, according to a study led by Agustín Sánchez-Lavega of the University of the Basque Country.
The discovery, confirmed by NASA’s Hubble Space Telescope and detailed in a September 2026 study published in Science Advances, reveals a 10-sided atmospheric wave encircling Saturn’s south pole—a geometric counterpart to the planet’s long-standing hexagon at the north. The decagon, spanning roughly 104,250 miles (167,820 km) in diameter, is the first such structure observed in Saturn’s southern hemisphere, with each side measuring about 10,425 miles (16,782 km). Researchers describe it as a vertically extended wave locked within a powerful jet stream, distinct from the hexagon’s stable, decades-old structure.
The Decagon’s Unique Structure
The decagon is not a surface feature but a visible manifestation of a wave within Saturn’s atmosphere, observed across multiple cloud layers. Hubble’s high-resolution imaging, combined with data from the Outer Planet Atmospheres Legacy (OPAL) program, showed the structure shifts slightly when viewed through different filters, indicating its depth. This vertical extension mirrors the hexagon’s behavior, which Cassini observations revealed persisted through seasonal changes. However, the decagon’s formation appears more recent, with hints of its presence dating to 2023 in Hubble archives.
Amateur Astronomers’ Role in the Discovery
The decagon’s identification began with ground-based observations by amateur astronomers Trevor Barry and Jean-Paul Oger, who contributed images to the Planetary Virtual Observatory Laboratory (PVOL). Their work, coordinated through the PVOL network, revealed subtle undulating patterns at Saturn’s south pole in 2024 and 2025. These hints prompted further analysis of Hubble data, which confirmed the structure’s emergence.
Simon, a co-author of the study and OPAL principal investigator, emphasized the importance of long-term observational programs. A decade of matched images is what turns 'there seems to be something at the pole' into a measurable wave with a countable number of sides,
she said. The OPAL program’s annual, consistently calibrated observations of Saturn and other outer planets enabled this discovery, highlighting the value of sustained, systematic data collection.
Why the Decagon Formed Now
The decagon’s sudden emergence raises questions about its formation. Unlike the hexagon, which has been observed for over 40 years, the decagon appears to have developed recently, with no evidence of a long-lived structure in Cassini data from 2004–2017. Researchers speculate that Saturn’s axial tilt and orbital dynamics may have recently aligned to create the conditions for this wave, though the exact mechanisms remain unclear.
The question is, why did it suddenly form now when we haven’t seen one before?
Simon asked. We need to understand how the decagon evolves—whether it will become unstable and break up, or become more stable as solar radiation increases, which will peak at its latitude of around 60 degrees south in 2032.
The team plans to use Hubble and the James Webb Space Telescope to study the decagon’s evolution, along with computer models, to unravel its origins.
Implications for Planetary Science
The discovery challenges existing theories about atmospheric dynamics on gas giants. Laboratory experiments with spinning fluids have produced similar polygons, but no definitive explanation exists for the decagon’s formation. The structure’s distinctiveness from the hexagon suggests that polygonal jets may arise under varying conditions, depending on factors like jet strength, temperature gradients, and atmospheric composition.
Saturn has a unique feature at the north pole, a hexagon. The fact that a decagon has formed at the south pole is a notable finding. The findings could inform future studies of Jupiter’s turbulent storms or exoplanetary atmospheres, where similar patterns might exist.
