Hubble detects ten-sided atmospheric wave at Saturn's south pole

NASA and collaborators announced that the Hubble Space Telescope has confirmed the presence of a decagon – a regular ten-sided atmospheric wave – encircling Saturn's south pole. The discovery, led by Agustín Sánchez-Lavega of the University of the Basque Country and published in Science Advances, marks the first large geometric jet pattern identified in the planet's southern hemisphere.

The finding contrasts with the well-known hexagonal jet stream at Saturn's north pole, first observed by Voyager in the 1980s and continuously documented for more than four decades. During the Cassini mission (2004-2017), the southern pole was surveyed in detail but showed only a circular vortex and no polygonal structure.

Saturn's 29.5-year orbital period means its seasons shift slowly. As the southern pole emerged from winter and became visible from Earth, amateur astronomers in Australia and France reported an undulating band in 2024 that sharpened into a clear ten-sided shape by 2025. Hubble images verified the pattern and, after reviewing archival data, the team traced its appearance to 2023, with no earlier detections.

"Neither earlier Hubble images nor any Cassini observations show the feature," Sánchez-Lavega said, indicating that the decagon likely formed after the spacecraft left Saturn's orbit.

The decagon sits within an eastward jet stream between roughly 58° and 63° south latitude and appears to be drifting eastward and strengthening, unlike the stationary hexagon. A nearby 4,000-kilometer anticyclone, dubbed a "Red Spot," may be influencing its development, according to the researchers' simulations.

The team emphasizes that continued monitoring will determine whether the decagon stabilizes like the northern hexagon or dissipates back into the surrounding jet stream.