Hubble Finds a Giant 10-Sided Wave Around Saturn’s South Pole

NASA’s Hubble Space Telescope has revealed an unexpected geometric feature in Saturn’s atmosphere: a giant, evolving 10-sided wave circling the planet’s south pole. Known as the decagon, the feature is not a solid object or a literal outline on the planet. It is a large-scale atmospheric wave shaped within one of Saturn’s powerful polar jet streams. 45

The decagon at a glance

The wave is about 13,000 kilometers (8,100 miles) across—slightly wider than Earth—and is centered near 63 degrees south latitude. Hubble’s Wide Field Camera 3 observed the structure at multiple wavelengths, allowing scientists to see it at different atmospheric altitudes. 34

That wavelength-dependent view matters: the decagon’s apparent position shifts slightly with wavelength, and the wave is visible through multiple layers of Saturn’s atmosphere. The result is evidence for a vertically extended atmospheric structure, rather than a pattern limited to the highest visible clouds. 45

NASA describes it as the first large, persistent regular-sided pattern observed in Saturn’s southern hemisphere. Observations collected over several years show that its outline has become more distinct since 2023. 3

A southern counterpart to Saturn’s hexagon—though not a twin

Saturn’s north pole is famous for its six-sided jet-stream feature, the hexagon, first identified in Voyager observations. The decagon is striking because it shows that Saturn can also produce a large polygonal wave around its opposite pole. 15

But the resemblance should not be mistaken for proof that the two structures are identical. The northern hexagon is a long-observed feature, while the southern decagon is newly recognized and still evolving. NASA notes that the differences between them may help researchers understand why polar jets can settle into distinct wave patterns. 35

How the wave emerged from the data

The southern pole was poorly placed for Earth-based observation during Saturn’s 2012–2023 winter. Once the viewing geometry improved, ground-based observers noticed an undulating southern-polar band, including imagery associated with amateur planetary observer Trevor Barry. Researchers then compared that clue with Hubble’s long-term observations to trace the decagon’s development. 35

The available record indicates that the feature was already present in 2023 and subsequently became more pronounced. Because the pole was hidden for much of the preceding period, however, the exact moment and mechanism of its formation were not directly observed. 35

What ten sides say about Saturn’s jet stream

The decagon sits inside a powerful southern jet stream. Its repeating, ten-lobed form shows that this jet can confine a large atmospheric disturbance into a coherent wave pattern rather than allowing it to disperse. 45

That geometry gives atmospheric scientists a useful constraint for models of Saturn’s circulation. A polygonal wave depends on conditions such as the jet’s speed, width, curvature, and behavior at different altitudes. Hubble’s observations therefore provide more than an unusual image: they offer a way to test explanations for how giant-planet jets organize themselves. 45

The observations do not yet establish why this particular wave has ten sides, or what triggered it. Its origin could involve an instability in the jet, deeper atmospheric dynamics, seasonal effects, or a combination of factors. For now, the evidence supports the decagon’s reality and vertical extent more strongly than any single explanation for its formation. 35

Why Cassini and future observations matter

NASA’s Cassini mission provided years of context on Saturn’s clouds, polar regions, and jet streams, but the newly recognized southern pattern is emerging from a later observing record. Comparing the decagon with Cassini-era observations and Saturn’s northern hexagon can help determine whether it is a newly formed feature, a recurring seasonal phenomenon, or a shorter-lived configuration. 5

Continued Hubble monitoring, observations with the James Webb Space Telescope, and atmospheric modeling will be important next steps. They may show whether the decagon reaches deeper into Saturn’s atmosphere, changes with the seasons, or settles into a durable pattern comparable to the northern hexagon. 5

For now, Saturn’s south pole has added a new mystery: a planet-scale, 10-sided wave that demonstrates just how structured—and still poorly understood—giant-planet weather can be.