Saturn's South Pole Reveals Giant Ten-Sided Atmospheric Wave
A massive, ten-sided atmospheric wave, a "decagon," has been discovered encircling Saturn's south pole, a feature previously unseen by NASA's Cassini spacecraft. The discovery was made using Hubble observations and confirmed by international astronomers.
Astronomers have detected a colossal, ten-sided atmospheric wave, dubbed a "decagon," encircling Saturn's south pole, a striking discovery published September 2 in Science Advances. The international research team, led by Agustín Sánchez-Lavega of the University of the Basque Country, utilized observations from NASA's Hubble Space Telescope to confirm the geometric pattern. This marks the first time such a large, regular polygonal jet stream has been observed in Saturn's southern hemisphere, adding another layer of complexity to the gas giant's famously dynamic atmosphere.
Saturn has long been known for its atmospheric oddities, most notably the stable, six-sided jet stream, or "hexagon," that has continuously encircled its north pole for over four decades. This northern phenomenon, first observed during the Voyager flybys in the early 1980s, is wider than two Earths and has been a source of scientific fascination. In contrast, NASA's Cassini spacecraft, which orbited Saturn from 2004 to 2017, meticulously mapped the southern pole. Cassini's extensive data revealed a powerful hurricane-like vortex at the center but no polygonal structure, leading scientists to believe the hexagon might be a unique anomaly.
A New Geometric Marvel Emerges
The recent discovery of the decagon presents a fascinating puzzle regarding the planet's atmospheric dynamics and Saturn's slow seasonal cycle. Saturn completes an orbit around the Sun approximately every 29.5 Earth years, meaning its seasons change at a glacial pace. For a significant portion of the Cassini mission, the planet's south pole was tilted away from Earth, shrouded in winter and difficult to observe in detail. However, as Saturn's seasons progressed and the south pole began to tilt back towards Earth's view in recent years, the planet revealed its newly formed atmospheric feature.
The breakthrough came when amateur astronomers, feeding data to the Planetary Virtual Observatory, noticed an unusual undulating band in 2024. Enhanced polar projections from images captured by observers in Australia and France in 2025 clearly defined the ten-sided shape. Hubble's high-resolution images corroborated these findings, tracing the decagon's presence back to 2023. Significantly, neither earlier Hubble images nor any of the data collected by the Cassini probe during its 13-year mission show any sign of this ten-sided structure.
This absence in the Cassini archive is considered crucial evidence by the researchers. "Because the probe documented the south pole so thoroughly and found no polygon, its archive converts a mere absence into evidence: the decagon is new, and its birth can be dated to a window after 2017," stated a co-author, Amy Simon of NASA Goddard. This implies that the continent-scale geometric structure assembled itself relatively recently, during the period when the south pole was not optimally observable from Earth.
Unlike the stationary and remarkably stable northern hexagon, the newly discovered decagon is part of an eastward-moving jet stream located between approximately 58 and 63 degrees south latitude. Researchers are particularly intrigued by the differences between the two polar polygons. The decagon is described as an evolving structure, dynamic rather than static, and appears to be strengthening. Further complicating the picture, a 4,000-kilometer anticyclone, which the team has nicknamed the "Red Spot," churns just north of the decagon. Simulations suggest this massive storm may play a role in sculpting the ten-sided wave, offering a potential glimpse into the formation process of such large-scale atmospheric patterns – something the hexagon, with its long-established stability, has not allowed.
The discovery highlights how complementary observational tools, including ground-based telescopes and dedicated space observatories, are essential for understanding planetary phenomena. While the Cassini mission provided unprecedented close-up views and data, its findings are now complemented by the observations of Hubble Space Telescope and the global network of amateur astronomers. The ongoing observation of Saturn's south pole will be key to determining whether the decagon settles into a long-term pattern similar to its northern counterpart or dissipates, offering further insights into the complex and ever-changing atmosphere of the ringed planet.