A New Shape on a Familiar Planet
Scientists have discovered an enormous 10-sided atmospheric wave, or decagon, circling Saturn's south pole. This massive weather pattern was identified in recent years using data from the Hubble Space Telescope, with the first signs appearing in images
from 2023. The discovery came as a surprise, as researchers had been searching for a southern counterpart to the famous northern hexagon since the 1990s without success. Even NASA's Cassini spacecraft, which orbited Saturn from 2004 to 2017, saw no evidence of such a stable geometric shape at the south pole, observing only a monstrous, hurricane-like vortex. The decagon's recent emergence was made possible by Saturn's long, slow seasons; as the planet's southern hemisphere tilted back toward Earth after more than a decade, this new feature came into view.
More Than Just a Cloud Pattern
This decagon is not merely a superficial pattern on the cloud tops. It's a massive atmospheric wave embedded deep within one of Saturn's powerful jet streams, which rushes eastward at speeds around 420 kilometers per hour. Observations at different wavelengths show the decagon extends vertically through multiple layers of the atmosphere, making it a towering, three-dimensional structure. Unlike a hurricane on Earth that might last a week, these planetary-scale waves can be remarkably persistent. The entire structure is vast, measuring roughly 167,820 kilometers wide. Scientists believe these kinds of polygonal shapes are formed by meandering jet streams; small disturbances cause the jet to wobble into a stable, geometric pattern. Laboratory experiments on Earth, using rotating tanks of liquid, have been able to replicate hexagons and other polygons, lending support to this theory.
The Hexagon vs. The Decagon
For over 40 years, Saturn's north pole has been defined by its hexagon, a six-sided jet stream roughly 32,000 kilometers wide that has remained remarkably stable. The new southern decagon provides a fascinating point of comparison. While both are polygonal waves in the atmosphere, they are distinctly different. The decagon has ten sides to the hexagon's six, is located at a less polar latitude, and appears to be a much newer, still-evolving feature. While the hexagon has been a steady presence for decades, the decagon seems to have formed only recently and is still growing stronger. This gives scientists a rare opportunity to watch a giant atmospheric pattern being born, something they never got to witness with the already-established hexagon.
The Mystery of Its Formation
The biggest question is why the decagon formed now and why it has ten sides instead of six. One leading hypothesis links its creation to a nearby storm. Just north of the decagon is a 4,000-kilometer-wide anticyclone—a swirling high-pressure vortex that researchers have nicknamed a "Red Spot," similar to Jupiter's famous storm. This vortex appeared to darken just before the decagon emerged, and the 10-sided wave is most pronounced near this storm, suggesting the vortex could be sculpting it. However, computer simulations have not yet been able to perfectly reproduce the decagon, and scientists remain cautious. A similar theory once linked the northern hexagon to a nearby vortex, but that storm eventually disappeared while the hexagon remained, proving the link was not so simple.
What This Means for Planetary Science
Studying these giant geometric patterns offers a window into the complex physics governing the atmospheres of gas giants. The discovery that Saturn can host two different, long-lived polygons at its poles challenges existing models of atmospheric dynamics. It suggests the planet's weather systems are even more complex and varied than previously understood. The fact that the south pole formed a decagon while the north formed a hexagon points to subtle differences in the conditions—such as wind structure or latitude—between the two poles. By observing how the decagon evolves as Saturn's southern summer progresses, scientists hope to unlock the secrets of how these colossal weather patterns form, stabilize, and eventually dissipate. This knowledge not only helps us understand Saturn but also provides insights into the atmospheres of other giant planets throughout our solar system and beyond.
