56 Saturn Decagon Facts - Hubble's 10-Sided Wave

By Share a Fact Editorial Team · Published September 6, 2026

What the Decagon Is

The decagon is a ten-sided wave in Saturn's atmosphere that wraps all the way around the planet's south pole.
It sits inside one of Saturn's fast eastward jet streams, at roughly 58 to 63 degrees south latitude.
Researchers describe it as a planetary-scale atmospheric wave in the jet rather than a cloud pattern riding on top of it.
Each of its ten sides is about 16,780 kilometres long, so the whole outline runs close to 168,000 kilometres.
Hubble records it at more than one wavelength, and its apparent position shifts slightly between filters because each filter probes a different altitude.
That shift shows the wave extends vertically through several layers of the atmosphere rather than a single cloud deck.
In Hubble images the band appears bluish, and the aerosols that give it that colour have not yet been identified.
It is the first large, regular-sided jet-stream pattern ever recorded in Saturn's southern hemisphere.

Hubble data from 2023 hold the earliest faint hints of a ten-vertex shape, although nobody recognised it at the time.
Amateur astronomers Trevor Barry and Jean-Paul Oger noticed an undulating band in ground-based images taken in 2024.
Their pictures were shared through the Planetary Virtual Observatory Laboratory, a website that gathers planetary photographs from observers worldwide.
Ground-based imagery through 2025 sharpened the band into a clearly defined decagon.
Hubble photographed the fully formed decagon on 29 August 2025.
The observations came from Hubble's Outer Planet Atmospheres Legacy programme, which images the outer planets every year.
The study was led by Agustín Sánchez-Lavega of the University of the Basque Country in Spain, with co-authors including Amy Simon of NASA Goddard and Michael Wong of UC Berkeley.
The results were published in the journal Science Advances on 2 September 2026.

The decagon drifts eastward at only about 2.5 metres per second, roughly 9 kilometres per hour.
The jet stream it sits in blows at about 116 metres per second, more than 400 kilometres per hour.
The pattern therefore moves far more slowly than the winds flowing through it, which is typical of a wave rather than a cloud being carried along.
The longitudes of its ten vertices swing back and forth with a period of about 32 days.
Those swings have amplitudes of between about 4.6 and 8.4 degrees of longitude.
An anticyclonic vortex lies just north of the wave, near 55 degrees south, and appeared in 2023 before darkening in 2025.
Cassini recorded a short-lived disturbance near 60.5 degrees south in 2004 that lasted only days, unlike the persistent decagon seen today.
Hubble's year-on-year images suggest the wave is still strengthening rather than fading.

Saturn's north pole is ringed by a six-sided jet-stream pattern identified by David Godfrey in 1987 from Voyager images taken in 1981.
The hexagon sits near 78 degrees north, much closer to the pole than the southern decagon.
Each side of the hexagon is about 14,500 kilometres long, and the whole figure spans roughly 30,000 kilometres.
Winds within the hexagon reach about 320 kilometres per hour.
Cassini imaged the hexagon in visible light from 2009 onward, having arrived at Saturn in 2004.
Between 2012 and 2016 the hexagon's interior changed from bluish to golden as seasonal sunlight built up haze.
The hexagon has persisted for more than 40 years and does not drift in longitude the way other clouds do.
Sánchez-Lavega's team had been searching for a southern counterpart since 1990 before the decagon appeared.

Cassini orbited Saturn from 2004 to 2017 and found no long-lived polygon at the south pole.
Earth-based observers could not see Saturn's south pole well between 2012 and 2023 because the planet's tilt hid it from view.
Jupiter's north pole holds a central cyclone surrounded by eight others arranged in a near-regular octagon, as seen by NASA's Juno spacecraft.
Jupiter's south pole had five cyclones around a central storm until a sixth appeared in November 2019 and turned the pentagon into a hexagon.
Each of Jupiter's northern polar cyclones is roughly 2,400 to 2,800 kilometres across, small next to Saturn's polar polygons.
Laboratory experiments at the University of Oxford reproduced polygonal jets in rotating tanks of fluid, producing shapes with three to eight sides.
Proposed explanations for Saturn's polygons include Rossby waves, wind-shear instabilities and the shielding effect of nearby vortices.
Sánchez-Lavega built a shallow-water model showing how a decagon can emerge in a turbulent rotating fluid.

Saturn's atmosphere is made mostly of hydrogen and helium.
Equatorial winds reach about 500 metres per second, or 1,800 kilometres per hour.
Saturn's equatorial diameter is about 120,500 kilometres, nine times that of Earth.
A Saturn day lasts about 10.7 hours, so its jet streams circle the planet quickly.
Saturn's axis is tilted 26.73 degrees, giving it seasons much like Earth's.
One Saturn year lasts about 29.4 Earth years, so each season runs for more than seven years.
Hubble's annual Outer Planet Atmospheres Legacy images have tracked Saturn's changing seasons since 2018.
Saturn has 274 confirmed moons as of March 2025, more than any other planet.

Scientists do not know why the decagon formed now after decades without a long-lived southern polygon.
The team cannot yet say whether it will settle into a stable shape like the hexagon or break up.
Sánchez-Lavega suggests the difference from the hexagon may come down to latitude, the background winds or the nearby high-pressure vortex.
Michael Wong has proposed that the vortex may have triggered the initial disturbance, after which a balance of forces locked in the decagon.
What lies beneath the visible cloud layers along the wave remains unknown.
The James Webb Space Telescope is planned to study the feature at infrared wavelengths.
Amy Simon said the strengthening wave gives researchers the rare opportunity to watch a giant atmospheric pattern develop.
Amateur observers remain part of the effort, because a discovery like this rests on years of repeated observations rather than a single image.