The remarkable structure is not a solid object or a perfectly fixed geometric shape. Instead, scientists describe it as an enormous atmospheric wave embedded within one of Saturn’s powerful jet streams. Hubble observations show that the feature extends through multiple layers of the planet’s atmosphere.
The discovery is particularly fascinating because Saturn is already famous for another geometric atmospheric phenomenon: the enormous hexagon at its north pole, which was first observed more than four decades ago. The newly identified southern decagon is the first large, regular-sided jet pattern observed in Saturn’s southern hemisphere.
When Did the Saturn Decagon Form?
Researchers reconstructed observations dating back to 2023 and found subtle evidence that the structure was beginning to emerge around that time. Ground-based observations in 2024 and 2025 provided additional clues before Hubble produced clearer views of the phenomenon.
Scientists believe the decagon may have developed relatively recently, but exactly why it formed now remains an unanswered question.
The feature is enormous. Reports describe individual sides stretching more than 10,000 miles, while the overall structure spans roughly 167,800 kilometres across. Unlike Saturn’s northern hexagon, the southern pattern appears to be evolving rather than remaining completely stable.
Why Is Saturn Forming Geometric Shapes?
Saturn’s atmosphere contains extremely powerful winds and rapidly moving jet streams. Scientists believe interactions between these atmospheric currents can create large-scale waves that develop into polygonal patterns.
However, researchers still do not fully understand why Saturn produces such striking geometric structures or why the newly discovered southern decagon appeared at this particular time.
The discovery gives scientists a rare opportunity to watch a planetary atmospheric pattern develop rather than simply studying one that has existed for decades.
NASA and researchers are expected to continue monitoring Saturn as its southern hemisphere becomes increasingly visible. Future observations could help determine the decagon’s three-dimensional structure, how long it will survive and what caused it to form.
For now, Saturn has added another extraordinary geometric mystery to its growing list of atmospheric phenomena — a gigantic decagon swirling around its south pole.
