Hubble caught a ten-sided jet wave assembling at Saturn's south pole

Hubble observations revealed a giant, evolving, 10-sided atmospheric wave encircling Saturn's south pole, the first time a large, regular-sided jet pattern has been observed in the planet's southern hemisphere.

In October 2023, researchers saw the first signs of the decagon wave in red-filtered images taken by the Hubble Space Telescope; further observations in 2024 and 2025 gave a clear picture of the pattern.

Hubble's view from space offers unmatched image sharpness and spatial resolution over full rotations of Saturn, without smearing by Earth's atmosphere.

It was in ground-based images contributed to the University of the Basque Country's Planetary Virtual Observatory Laboratory website, first in 2024, that Sanchez-Lavega and amateur astronomers Trevor Barry and Jean-Paul Oger noticed a subtle undulating band along the southern pole; additional 2025 ground-based imagery hinted more strongly at the decagon structure.

Researchers used shallow water model simulations representing a simplified version of Saturn's troposphere, the lowest atmospheric layer where weather patterns are shaped.

Agustin Sanchez-Lavega, lead author of the new study, is a researcher at the University of the Basque Country in Spain.

The researchers concluded the wave may have been created by a spatially periodic disturbance in a zonal jet stream, or driven by a swirling vortex that might be near a Red Spot slightly to the north.

Sanchez-Lavega said the team had been searching Hubble images for a southern counterpart to Saturn's northern hexagon since 1990, that images from Cassini, which orbited Saturn between 2004 and 2017, showed no inkling of a long-lived formation either, and that the Hubble data confirmed the feature's presence back to 2023.

The discovery was possible because Saturn's changing seasons gradually brought the planet's south pole back into view from Earth, where astronomers analysing ground-based observatory images first identified it.

The team plans to continue observing Saturn to determine whether the decagon settles into a long-lived, stable configuration like the northern hexagon or continues to evolve.

The wave sits within one of Saturn's powerful jet streams and extends through multiple layers of the atmosphere, indicating it is not just a cloud-level feature but a vertically extended atmospheric structure.

The decagon's apparent position shifts slightly because Hubble captures images at different wavelengths, and those wavelengths probe different altitudes in Saturn's atmosphere.

Saturn's six-sided northern polar wave was revealed in images taken during Voyager flybys in 1980 and 1981 and has persisted for over 40 years without substantial changes.

Study co-author Mike Wong of the University of California, Berkeley said many OPAL discoveries are based not on one observation but on years and years of data, and that regular observations over time are enabling new findings.

According to NASA, Earth's atmosphere lacks such symmetric polygonal structures partly because Earth receives nearly 100 times more sunlight than Saturn and has a non-uniform surface with mountains disturbing atmospheric flow, while Saturn has no solid surface and a far more uniform composition.

Cassini's time in Saturn orbit spanned 13 years.

The count of known regular polygonal polar jet patterns on Saturn goes from one to two with this study.

Amy Simon, OPAL principal investigator at NASA's Goddard Space Flight Center and a study co-author, said the northern hexagon has been there every time they looked for more than 40 years, while the new feature appears to be strengthening, giving a rare opportunity to watch a giant atmospheric pattern develop.

Simon said the most intriguing part is that the feature seems to have just formed recently, and the question is why it suddenly formed now when no such feature had been seen before.