Saturn has just revealed a new curiosity: a gigantic ten-sided figure is taking shape in its atmosphere around the south pole.
Saturn is a giant planet composed mainly of gas. The observed shape corresponds to a huge atmospheric wave caught in a band of very fast winds. Viewed from above the pole, this wave forms ten sides, hence its name: decagon.
Saturn observed by Hubble on August 29, 2025, with a view of the south pole showing the ten-sided atmospheric wave.
Credit: NASA, ESA, STScI, A. Sánchez-Lavega, A. Simon, M. Wong; processing: A. Pagan.
The discovery immediately brings to mind another feature of Saturn. Its north pole is surrounded by a famous hexagon, a six-sided structure observed for more than 40 years. Astronomers had long been searching for a comparable phenomenon in the southern hemisphere, without finding one. Images from the Cassini spacecraft, taken through 2017, had revealed no lasting structure of this kind in particular.
The situation changed with new observations. Amateur astronomers spotted a slight ripple around the south pole in 2024. Researchers then examined images from the Hubble Space Telescope. They discovered that the shape was already perceptible in 2023, then became more distinct over observations carried out through 2025.
This decagon therefore does not appear to be merely a temporary arrangement of a few clouds. Hubble observes Saturn at several wavelengths, making it possible to examine different altitudes in its atmosphere. The shape appears at several of these levels. The wave therefore extends vertically through the atmosphere and accompanies a powerful band of winds.
View of Saturn’s south pole by Hubble through an infrared filter, where the atmospheric decagon is clearly visible.
Credit: NASA, ESA, STScI, A. Sánchez-Lavega, A. Simon, M. Wong; processing: A. Pagan.
Another difference from the northern hexagon is that the new pattern still appears to be evolving. Observations indicate that it has strengthened since 2023. Researchers do not know precisely when it appeared, because the south pole was difficult to observe from Earth during the preceding years. Its formation may therefore have occurred between Cassini’s last observations and its return to the field of view of ground-based telescopes.
The question remains why Saturn’s winds take on such a regular geometric shape. A band of winds can ripple instead of following a perfect circle. Under certain conditions, these ripples can form several large segments. Models will now have to explain why ten sides appear in the south, while six have persisted for decades in the north.
Researchers will continue monitoring the decagon with Hubble and also hope to study it with the James Webb Space Telescope. Future observations will show whether its ten sides remain stable, shift position, or eventually disappear. They will also help determine whether this new structure can last for several decades, like the hexagon at the north pole.