Saturn Grew a Moving Decagon—Its Famous Hexagon Is No Longer Alone

On September 2, 2026, astronomers unveiled a giant, evolving, ten-sided atmospheric wave encircling Saturn’s south pole in Hubble Space Telescope observations. The Associated Press account of the discovery says the decagon migrates eastward at about 10 kilometres per hour, one side exceeds 16,700 kilometres, and the practically stationary northern hexagon has been visible to spacecraft for more than 40 years.

The finding does not reveal the decagon’s precise moment of formation. It shows a southern pattern emerging and becoming clearer across several observing seasons, creating a second polar polygon that differs from the northern benchmark in side count, motion, apparent stability, scale and known lifetime.

The decagon emerged across a multi-year observing record

The feature was reconstructed rather than captured at birth. NASA’s September 2 Hubble release traces subtle signs of the wave to Hubble data from 2023, an undulating band noticed by researchers and amateur astronomers Trevor Barry and Jean-Paul Oger in ground-based images from 2024, and clearer evidence in further imagery from 2025; it also notes that Cassini observations from 2004 to 2017 showed no comparable long-lived southern formation.

Saturn’s seasons made that sequence possible. As the planet’s south-polar region gradually returned to view from Earth, observers could inspect a region that had been poorly placed for sustained monitoring. Hubble then supplied sharp images over complete rotations of Saturn without the atmospheric blurring that affects ground-based telescopes.

This distinction matters for the headline’s verb “grew.” Astronomers observed the structure strengthening into a recognisable polygon, but they did not watch an unambiguous formation event from beginning to end. The wave may have developed while the south pole was difficult to see, and the available images cannot yet establish an exact birth date.

The southern polygon moves while the northern one holds position

The clearest north–south difference is motion. Both shapes are waves associated with powerful eastward jet streams, but the northern hexagon remains almost fixed relative to Saturn’s rotation. The southern decagon drifts eastward, while its corners meander and do not maintain the same regular appearance.

Size comparisons require more care. The reported length of a southern side establishes that the new feature is enormous, and current accounts describe it as larger than the northern polygon. However, the available public reports do not provide matched diameter measurements calculated with one method, so they do not support a precise percentage difference.

Stability is an even less symmetrical comparison. Decades of observations have already demonstrated the hexagon’s persistence, whereas the southern record covers only the decagon’s recent emergence. Its changing vertices may indicate that it is still developing, but only continued monitoring can establish whether it will settle, break apart or disappear.

Different wavelengths reveal a vertically extended wave

The decagon is not merely an outline on one visible cloud layer. Hubble filters sampling different wavelengths detect the boundary at different atmospheric altitudes, showing that the wave extends vertically through Saturn’s clouds and hazes. Its apparent position shifts slightly between those views because each wavelength probes a different level.

That altitude-dependent displacement is separate from the polygon’s eastward migration. The first describes how the boundary appears in different vertical layers at a given observing period; the second describes the overall pattern moving relative to the rotating planet.

The observations therefore establish vertical structure in the south, but they do not yet yield an equivalent depth profile for both polygons. Researchers still need to determine how far each wave reaches beneath the visible atmosphere and whether the northern and southern structures couple to deeper circulation in the same way.

A second polygon changes the scientific comparison

Before this discovery, Saturn’s hexagon could be treated as a singular atmospheric curiosity. A regular polygon now exists in each hemisphere, shifting the question from why Saturn has one exceptional shape to why the same planet can produce two polar waves with different geometries and behaviour.

No proposed mechanism yet explains all of those properties. Scientific American’s report on the competing hypotheses describes possible instability in the southern jet, forcing from deeper atmospheric levels and influence from a nearby high-pressure storm; it also notes that seasonal sunlight could strengthen the feature as illumination near its latitude approaches a peak around 2032.

Those possibilities remain hypotheses rather than confirmed causes. A successful explanation must account for the southern wave’s ten sides, slow drift and changing vertices while also explaining why the northern jet supports a stationary six-sided pattern with a much longer observational history.

Longevity is now the decisive unknown

Future observations can test whether the decagon becomes more regular as southern illumination increases or instead loses its polygonal form. Hubble, the James Webb Space Telescope and ground-based observers can also follow the boundary at different wavelengths, helping researchers separate changes over time from differences among atmospheric layers.

For now, the discovery itself is secure but the outcome is open. Saturn supports regular-sided atmospheric waves at both poles, so the famous northern hexagon is no longer an isolated example; the southern decagon’s motion, evolution and short record prevent scientists from calling the two structures stable twins.

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