A Ten-Sided Surprise
Astronomers have discovered a massive atmospheric wave with ten distinct sides, known as a decagon, encircling Saturn’s south pole. Announced in early September 2026, this discovery marks the first time a large, regular-sided jet pattern has ever been
observed in the planet’s southern hemisphere. The feature, a powerful jet stream that extends deep into the planet’s atmosphere, was identified using images from the Hubble Space Telescope. By analyzing data from Hubble’s Outer Planet Atmospheres Legacy (OPAL) program, scientists were able to trace the decagon’s emergence, noting it first started to form in observations from 2023 before becoming a more defined shape by 2025.
The Famous Northern Twin
For decades, Saturn’s geometric weather was thought to be a one-off phenomenon. Since the Voyager spacecraft flew past the planet in the early 1980s, scientists have been fascinated by a massive, six-sided jet stream at its north pole, famously known as “the hexagon.” This northern hexagon, wide enough to fit two Earths inside it, has remained remarkably stable for over 40 years, a permanent fixture in the planet’s cloudy skies. Scientists have long wondered if this bizarre structure was a unique fluke or if a southern counterpart might exist. For years, the answer appeared to be no.
A Planetary Game of Hide-and-Seek
The reason this southern decagon is a new discovery is a matter of timing and planetary mechanics. NASA’s Cassini spacecraft orbited Saturn from 2004 to 2017, providing an unprecedented look at the planet. During its entire 13-year mission, Cassini mapped the south pole in detail and found no trace of a persistent, regular-sided storm. This confirmed that the decagon is a recent development, forming sometime after Cassini’s mission ended. Furthermore, due to Saturn's 29-year orbit and axial tilt, its south pole was tilted away from Earth's view for many years. It only recently became visible again, allowing Hubble to spot the newly formed pattern.
More Than Just a Shape
The discovery of a second polygon storm suggests that the northern hexagon isn’t as unique as once believed. It indicates that these geometric jet streams might be a more fundamental feature of gas giant atmospheres under the right conditions. Unlike the stable northern hexagon, the southern decagon appears to be evolving, with its shape and strength changing in the years since it was first spotted. This gives scientists a rare opportunity to watch a giant atmospheric pattern develop in real-time, offering new clues into the powerful forces that shape weather on other worlds. Researchers are now trying to understand what triggered its formation, with some theories pointing to disturbances from nearby storm systems.
