A polar decagon on Saturn
Images from the Hubble Space Telescope have revealed a decagon of clouds around Saturn's south pole, which only formed in 2023 and continues to persist. It resembles the polar hexagon at the north pole, which has been known for more than 40 years.
Since the flybys of the two Voyager space probes in 1980 and 1981, the polar hexagon at Saturn's north pole has been known—a structure that has remained stable in the gas giant's cloud cover for decades. Now, a similar structure, a decagon, has been detected in the planet's southern hemisphere in images from the Hubble Space Telescope. This, too, is a cloud structure, but unlike the north polar hexagon, it only developed starting in 2023 and is still visible. It could continue to evolve.
Source: NASA, ESA, A. Sánchez-Lavega (Basque Country University, EHU)
Both structures were likely created by standing waves in deeper layers of the gas giant's atmosphere. The corners of the decagon appear to oscillate with a period of 32 days around their respective longitudes, with fluctuations of 4.6 to 8.4 degrees. It extends between 58 and 63 degrees south latitude and moves eastward at a speed of 2.5 meters per second (9 kilometers per hour), much slower than a jet stream at 60.5 degrees south latitude, which blows at 116 meters per second (418 kilometers per hour). The decagon could be caused by the jet stream and held in place at its southern latitude, or by a storm vortex located further north. Further observations with Hubble will need to clarify this.
In the coming months and years, the south pole of Saturn, which is tilted at 27 degrees to its orbit, will turn more and more toward the Sun, so that the southern decagon will become better illuminated and more clearly visible. With suitable space telescopes like Hubble or James Webb, further images of the new phenomenon in the ringed planet's atmosphere can be captured if it persists. Despite Saturn's seemingly calm appearance in the telescope, the weather there is very dynamic. However, due to low contrast, it is far less easy to track than on its inner neighbor, Jupiter, with its colorful bands.
Source: NASA, JPL / Caltech / ssI
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