Saturn's Decagon: What Hubble Found at the South Pole

The images that land on the server at the University of the Basque Country in Bilbao come from everywhere. A portal called the Planetary Virtual Observatory Laboratory has spent years collecting what people photograph of the solar system with private telescopes — from backyards in Australia, from French mountainsides, from front lawns in Ohio. Most of those images disappear into the archive. They are raw material, not an event.

In 2024 there was one among them that was different. Agustín Sánchez-Lavega, a planetary scientist in Bilbao, saw a fine, rippled band along Saturn's south pole in frames taken by the amateur astronomers Trevor Barry and Jean-Paul Oger. Not spectacular. A suggestion, nothing more — the kind of structure you talk yourself into when you have been looking long enough.

Sánchez-Lavega had a good reason not to look away. He had been hunting for exactly this since 1990. Saturn's north pole has worn a hexagon of clouds for more than four decades, larger than Earth, as stable as architecture. The south pole wore nothing. Why a planet grows a perfect geometric figure on one end and not the other is one of the more stubborn questions in planetary science — and there was a good answer to it. The answer was: because physically it cannot happen there.

On September 2, 2026, Science Advances published the paper that took that answer back. It is called "A decagon wave around Saturn's south pole." A ten-sided figure. It is new, it is sharpening, and according to the best available model it should not have formed.

What has stood at the north pole since 1980

To understand why the decagon is news, you have to know the hexagon.

When Voyager 1 and Voyager 2 flew past Saturn in 1980 and 1981, they sent back images of the north pole that looked at first glance like an error. Around the pole ran no vortex, no ring, no spiral — but a hexagon. Six straight edges, six corners, close to regular. The astronomer David Godfrey worked through the data and published the first systematic description in the journal Icarus in 1988.

The scale is hard to hold in the head. The hexagon measures roughly 18,600 miles (about 30,000 kilometers) edge to edge — each single side is longer than the diameter of Earth. It is not a cloud pattern painted on the surface but a jet stream, a band of wind running in that shape, at speeds around 200 miles per hour. Cassini measurements showed the six-fold structure reaching more than 180 miles upward, from the cloud deck into the stratosphere. At the center sits a polar vortex of its own, roughly 1,200 miles across — a storm in the eye of the figure.

Cassini orbited Saturn from 2004 to 2017 and accompanied the hexagon for thirteen years. In that time it shifted color from a cool blue to a gold tone, probably a consequence of Saturn's seasonal change and the photochemistry that came with it. The shape, though, held. It was there in 1980, it was there in 2017, and it is there today.

That persistence is precisely the puzzle. On Earth, weather systems last days. Jupiter's Great Red Spot, the famous counterexample, is a vortex — a round thing that holds itself together. A hexagon is something else. A hexagon has corners, and corners are the least likely thing in a flowing fluid.

Why the south stayed empty — and a model that predicted exactly that

In 2004, its first year at Saturn, Cassini turned its cameras on the entire southern hemisphere. No counterpart to the hexagon was found. What was found was a short-lived disturbance: the eastward wind band at 60.5 degrees south latitude showed a polygonal deformation for a few days — and vanished again. Through the end of the mission in 2017, when Cassini was deliberately steered into Saturn's atmosphere, it did not come back.

In 2010 a group around Ana Claudia Barbosa Aguiar and Peter Read at the University of Oxford produced the most convincing explanation to date — and it came out of a tank of water. The researchers put a 30-liter cylinder of water on a slowly rotating table; the water stood in for an atmosphere rotating with its planet. Into the cylinder they set a small ring that turned faster than the tank, creating an artificial jet stream, made visible with green dye.

The result, published in Icarus in 2010: the edge of the faster current breaks into polygons. And you can steer which one. The greater the speed difference between ring and tank, the fewer corners the figure has. The authors read the long-lived Saturn polygons as wave modes arising from the nonlinear equilibrium of barotropically unstable wind bands — put plainly: a jet stream shearing against calmer air goes unstable, and the instability locks into a standing wave with a whole number of crests. Six crests, six corners.

In the same paper they ran Saturn's wind profile through the model. The result was unambiguous: it matched the presence of the hexagon in the north — and the absence of a counterpart in the south. The asymmetry was not an accident and not an observational gap. It was a result.

Sixteen years later there is a decagon in the south.

August 29, 2025: the image

After the hint in the amateur frames, Sánchez-Lavega went to the OPAL team. OPAL stands for Outer Planet Atmospheres Legacy — a program that has spent more than a decade photographing Jupiter, Saturn, Uranus and Neptune every year with Hubble's Wide Field Camera 3. It grew out of a simple annoyance: in 2011 and 2013 there were no Hubble images of Jupiter at all. Amy Simon at NASA's Goddard Space Flight Center pushed through an annual inventory. Saturn joined in 2018, after the end of the Cassini mission.

Hubble sees more sharply than any instrument on the ground, because no shimmering air sits in between, and it can follow a full Saturn rotation. When the 2024 and 2025 frames were reprojected into a polar view — you project the sphere from above and subtract the mean brightness of each latitude band so the structure steps out of the contrast — the decagon was there. Not hinted at. Visible.

The key image is a mosaic from August 29, 2025, taken over several hours and projected onto the south pole. The pole itself is still in polar night at that point; the decagon sits at the edge of the dark region, at roughly 63 degrees south. In a single filter, F763M, it stands out with ten edges clearly enough that it no longer requires interpretation.

Working backward through the archives, the structure could be traced to 2023. Back then it was a smudge. In 2024 it grew clearer. In 2025 it sharpened its corners. That is the real difference from the north, and it is why specialists sat up: the hexagon was always already there. With the decagon, you can watch it form.

"A few years ago this feature wasn't there," Michael Wong of the Space Sciences Laboratory at the University of California, Berkeley, is quoted as saying in his institute's release. "It shows how important regular observation of the outer planets is."

What was actually measured

The numbers from the study are where fascination and evidence can be told apart. They are concrete enough to be checked.

The decagon runs between 58 and 63 degrees south latitude. It drifts east at about 2.5 meters per second — roughly 5.5 miles per hour, walking pace on a planet. The jet stream it sits in blows at 116 meters per second at 60.5 degrees south, better than 250 miles per hour. The figure therefore moves almost fifty times slower than the air it is made of. That is the signature of a standing wave: the pattern stays, the material flows through it.

The corners do not hold still. They swing around their respective longitudes with a period of 32 days and excursions between 4.6 and 8.4 degrees. The wave breathes.

Observations at different wavelengths show the structure is three-dimensional. Because different filters look into different altitudes of the atmosphere, the apparent position of the decagon shifts slightly by filter — an indication that this is not a pattern in one cloud deck but a vertically extended object. The visible part lies in the upper troposphere and is blue. What the aerosols producing that color are made of is unknown. How far down the wave reaches is unknown too.

One detail stands out. Slightly north of the decagon, at around 55 degrees south, sits an anticyclonic vortex. It was first observed in 2023 — the same year the wave is first faintly visible. In 2025 that vortex darkened sharply, shortly before the decagon took on its clear shape. "Maybe the vortex caused the initial disturbance, and then the force balance produced the persistent decagon," Wong says. "We really need more detailed simulations of the three-dimensional structure to be sure."

Sánchez-Lavega has developed a shallow-water model showing how a decagon can arise in a turbulent fluid. A model that can produce a shape, though, is not yet an explanation of why it appeared now.

Why polygons at all?

The question sounds more esoteric than it is. Corners in a fluid are nothing mystical; they are the visible result of an instability that limits itself.

Picture two air masses sliding past each other. The boundary between them is never smooth; every small disturbance gets amplified by the shear. On Earth you see the result in the jet stream, which meanders in long arcs. On a rotating planet that meandering wave cannot grow arbitrarily long — it has to close around the pole. And anything that closes can only have a whole number of crests. Six. Or ten. Not six and a half.

When that wave finds an equilibrium in which it neither dissipates nor keeps growing, it stands still while the air streams through it. The corners are where the crests sit. From far away it looks like drawn geometry. Up close it is a compromise between friction, rotation and inertia.

The Oxford experiment demonstrated exactly that in a water tank — and with it, why the number of corners is not arbitrary. It is a consequence of the wind profiles. Which is precisely why the 2010 prediction of "no southern counterpart" was not sloppiness but a clean result from the wind data known at the time. That the south has apparently changed since is the actual news. Something about the flow structure of the southern hemisphere is different today than it was in 2004.

The likeliest candidate for the "why now" is Saturn's season. The planet is tilted 27 degrees to its orbital plane; a Saturn year runs about 29.5 Earth years, so a season lasts a good seven. Spring has begun in the southern hemisphere. Cassini watched the south in summer; Hubble sees it now in a different phase. Whether that is the cause, or merely the condition under which we could look properly for the first time, is open.

The timeline

Year	What happened	Standing
1980/81	Voyager 1 and 2 photograph the hexagon at the north pole.	Verified
1988	David Godfrey gives the first systematic description in Icarus.	Verified
2004	Cassini finds only a few days' polygonal disturbance in the south, at 60.5 degrees south.	Verified
2010	Oxford tank experiment makes polygons — and predicts the absence of a southern hexagon.	Verified
2017	Cassini ends with its planned descent into Saturn's atmosphere. No southern polygon seen.	Verified
2023	First faint traces of the decagon in Hubble data; an anticyclone at 55 degrees south becomes visible.	Verified
2024	Amateur frames in the PVOL portal show a rippled band. Sánchez-Lavega follows it up.	Verified
Aug 29, 2025	Hubble mosaic shows the decagon clearly at around 63 degrees south.	Verified
Sep 2, 2026	Publication in Science Advances; NASA and ESA announce the discovery.	Verified

The other Saturn: why this shape makes people uneasy

Honesty requires naming the second reason this story is traveling. It has nothing to do with atmospheric physics.

Saturn is not a neutral body in the European history of ideas. It was the outermost planet visible to the naked eye — the boundary of the system, literally the end of the known world. That burned itself into the attributions. To the Romans he was the god of the December Saturnalia, a festival of inverted order; in the Greek equivalent, Kronos devours his own children. In alchemy he is assigned lead: heavy, dull, the basest of metals and at the same time the starting material of every transformation. In the doctrine of the temperaments he owns melancholy — that compound of heaviness and insight whose history Raymond Klibansky, Erwin Panofsky and Fritz Saxl traced in their study Saturn and Melancholy, all the way to Dürer's engraving Melencolia I.

Anyone who associates Saturn with limit, weight and testing stands in a very old and well-documented line. We have written that out for practice elsewhere, in the piece on the Saturn return, and for the metals in spiritual alchemy.

Then there is a second layer, and it is younger than it pretends to be. Ever since the hexagon of 1980, an observation has circulated: a regular hexagon is exactly what you see when you look at a cube along its space diagonal. That is mathematically correct. Lay a plane perpendicular to the space diagonal through the center of a cube and the cross-section is a regular hexagon. From that pretty geometric fact the internet regularly draws a conclusion that is not one — that black cubes in religion and architecture point to a worldwide Saturn cult.

There are no sources for that. The Kaaba in Mecca was a pre-Islamic sanctuary; that is not in dispute. A demonstrable connection to a Saturn cult does not exist, and the chief deity of the pre-Islamic Quraysh was not Saturn. Black cubic forms recur across architectural and art history because the cube is the simplest stable basic form there is. Anyone building a chain out of that is building it from resemblances, not from evidence. Parts of these narratives also tip into antisemitism. This magazine wants nothing to do with that, and we are writing it down here so it is not left unsaid.

The interesting thing is that the fascination carries without the superstructure. That a gas planet forms regular polygons is astonishing enough. And that we find six-fold order in honeycomb, basalt columns, snow crystals and now on Saturn is not a message but a statement about mathematics: certain boundary conditions force certain forms, regardless of whether wax, lava, water or hydrogen is inside. If you want to follow that, the symbol side is at sacred geometry — with the same separation of measurement from meaning that applies here.

What is in the videos, and what is in the data

One correction, because it keeps recurring. In coverage over recent weeks, the decagon is occasionally relocated to the north pole, or presented as though the hexagon had turned into a decagon. Neither is true.

The hexagon is at the north pole, unchanged. The decagon is its own, new structure at the south pole. It replaces nothing. It is the first large-scale, regular jet-stream figure ever observed in the southern hemisphere — and both exist at the same time right now. That is more remarkable than any mix-up: Saturn is wearing two polygons, one at each pole, with different corner counts, different ages and different behavior.

What we don't promise

Nothing in this piece is a statement about you. A wave in Saturn's atmosphere does not affect your week, your mood or your decisions, and we are not going to suggest otherwise. What is documented is a tradition of interpretation — Saturn as limit, time, lead and melancholy — and a tradition of interpretation is a cultural fact, not a physical one. We keep those two apart on purpose, here and everywhere in this magazine.

We also do not promise that the decagon will last. It may sharpen for another decade or dissolve in three years. Nobody knows, and any piece telling you otherwise is filling a gap in the record with confidence.

The open question

Over the coming years Saturn's south pole turns further toward the sun. The decagon, which today sits at the edge of polar night, will be better lit and easier to see. Hubble will keep looking; the James Webb Space Telescope can measure in wavelengths Hubble cannot reach.

And then there is the question that will not compute away. If a model working from measured wind data correctly predicts the absence of a structure — and the structure appears sixteen years later anyway — then either the planet has changed or our picture of it has. Amy Simon puts it in the NASA release as dryly as only a scientist can: "The question is why it suddenly formed now, when we never saw one before."

There is no answer to that. Not in the study, not in the press releases, not here. A decagon whose edges measure multiples of Earth formed between two observations, in a place where the best available theory had ruled it out, and nobody can say whether it will still be there in five years. That is not a failure of science. That is the rare moment when it admits it is currently watching.

Frequently asked questions

What is the decagon on Saturn?
A ten-sided wave structure in Saturn's atmosphere around the south pole, found in images from the Hubble Space Telescope and published on September 2, 2026 in Science Advances. It lies between 58 and 63 degrees south latitude, drifts east at about 2.5 meters per second and extends through several layers of the atmosphere.

Has the hexagon at the north pole disappeared?
No. The north polar hexagon has been documented since the Voyager flybys of 1980 and 1981 and stands unchanged. The decagon is its own, new structure in the southern hemisphere. Saturn is currently wearing both figures at once.

Why does a gas planet form corners at all?
Because a fast jet stream shearing against slower air goes unstable and locks into a standing wave. Since that wave has to close around the pole, it can only have a whole number of crests — and those appear as corners. In the lab it can be reproduced in a rotating water tank with a faster-spinning inner ring; the number of corners depends on the speed difference.

Why was the decagon only found now?
Because in this form it did not exist before 2023. Cassini observed the south pole from 2004 to 2017 and, apart from a disturbance lasting a few days in 2004, found nothing comparable. In Hubble data the structure can be traced back to 2023 and has sharpened year by year since. On top of that, Saturn's seasons are only gradually turning the south pole back into view.

Is there an ancient cult behind the Saturn hexagon?
There are no sources for it. What is demonstrable is that Saturn stands for limit, time, lead and melancholy in the European history of ideas — a documented line from antiquity through alchemy to Dürer. It is also demonstrable that a cube viewed along its space diagonal appears as a regular hexagon. Deriving from that a historical Saturn cult still operating today is a conclusion without evidence.

How big is the hexagon at the north pole?
Roughly 18,600 miles across; each single edge is longer than the diameter of Earth. The jet stream that carries it blows at about 200 miles per hour, and the six-fold structure reaches more than 180 miles in altitude, from the cloud deck into the stratosphere. At the center sits a polar vortex around 1,200 miles wide.

Sources and further reading

• NASA: "NASA's Hubble Tracks New Decagon Encircling Saturn's South Pole," September 2, 2026 — Goddard Space Flight Center release, with the quotes from Amy Simon and Agustín Sánchez-Lavega.
• ESA/Hubble: "Hubble tracks new decagon encircling Saturn's south pole" (heic2612), September 2, 2026 — European release with image material.
• UC Berkeley Space Sciences Laboratory: "Decagon wave emerges near Saturn's south pole," September 2, 2026 — background on OPAL, the anticyclone at 55 degrees south and the Michael Wong quotes.
• A. Sánchez-Lavega et al., "A decagon wave around Saturn's south pole," Science Advances, September 2, 2026, DOI 10.1126/sciadv.aee4251.
• A. C. Barbosa Aguiar, P. Read et al., "A laboratory model of Saturn's North Polar hexagon," Icarus 206 (2010), pp. 755–763, DOI 10.1016/j.icarus.2009.10.022 — the tank experiment and the prediction of no southern counterpart.
• D. A. Godfrey, first systematic description of the north polar hexagon, Icarus 76 (1988).
• R. Klibansky, E. Panofsky, F. Saxl, Saturn and Melancholy — on the history of ideas.
• More in the magazine: Sacred geometry · Saturn return · Quantum physics and spirituality