Saturn's Southern Secret: How Hubble Uncovered a Ten-Sided Storm at the Bottom of the Ringed World
For nearly four decades, Saturn's north pole has hosted one of the solar system's strangest and most photogenic weather features: a colossal, perfectly hexagonal jet stream that has churned around the pole since it was first glimpsed by the Voyager spacecraft in the early 1980s. Scientists have marveled at the hexagon's stability, its crisp geometric edges, and its refusal to drift, dissolve, or deform even as decades passed and seasons changed. For just as long, one obvious question lingered in the background: was there anything like it waiting at the other end of the planet?
For years, the answer appeared to be no. Saturn's south pole, studied by the Cassini spacecraft during its thirteen years in orbit between 2004 and 2017, showed nothing resembling the northern hexagon — just a swirling, comparatively featureless polar vortex. Earlier Hubble observations going back to 1990 turned up nothing either. It seemed as though Saturn's atmosphere played by different rules in each hemisphere, and the hexagon was a one-of-a-kind curiosity rather than evidence of a universal, symmetry-loving process buried in the planet's turbulent jet streams.
That assumption no longer holds. In new research published in the journal Science Advances, a team of planetary scientists working with NASA's Hubble Space Telescope has announced the discovery of a giant, evolving, ten-sided atmospheric wave now encircling Saturn's south pole. Researchers are calling it the "decagon," and it represents the first large, regular-sided jet pattern ever documented in Saturn's southern hemisphere. It is, in the plainest sense, a sibling to the famous northern hexagon — but one that appears to be far younger, considerably less stable, and possibly still in the process of being born.
A Feature That Wasn't Always There
What makes the decagon such a remarkable find is not just its shape, but its apparent age. Unlike the hexagon, which has been a fixture of Saturn's northern hemisphere for as long as humanity has had the instruments to see it, the decagon seems to be a genuinely new phenomenon. By stitching together several years of Hubble images collected through its Outer Planet Atmospheres Legacy program — known by the acronym OPAL, which has photographed Jupiter, Saturn, Uranus, and Neptune annually for more than a decade — researchers traced faint, subtle hints of the pattern as far back as 2023. At that point it was barely perceptible, a slight undulation buried in the noise of Saturn's turbulent polar clouds. By 2024 and 2025, the wave had sharpened into an unmistakable, ten-sided geometric shape wrapping around the pole at roughly 63 degrees south latitude.
This timeline matters enormously to planetary scientists, because it means they may be watching a large-scale atmospheric structure assemble itself in something close to real time — an exceptionally rare opportunity in planetary science, where most "permanent" atmospheric features are already fully formed by the time telescopes powerful enough to resolve them come online. Amy Simon, an OPAL principal investigator based at NASA's Goddard Space Flight Center, has described the moment as unprecedented for Saturn's southern hemisphere, noting that the sheer persistence of the northern hexagon across more than 40 years of observation stands in sharp contrast to a feature that appears to be actively strengthening before scientists' eyes. Rather than a settled, ancient structure, the decagon looks like a work in progress — and nobody yet knows what its final, if any, resting state will look like.
How a Global Community of Stargazers Found It First
The decagon's discovery is also a story about the enduring value of ground-based, amateur, and citizen astronomy working hand-in-hand with a flagship space telescope. Saturn's axial tilt means that for years at a time, the planet presents one pole or the other more favorably toward Earth, and only as the planet's decades-long seasonal cycle gradually swung its southern hemisphere back into view did astronomers on the ground get a good enough look to notice something odd.
Agustín Sánchez-Lavega, an astrophysicist at the University of the Basque Country in Spain and the lead author of the new study, maintains a website called the Planetary Virtual Observatory Laboratory, which accepts and aggregates images of solar system planets submitted by observers across the globe — a mix of professional researchers and dedicated amateur astronomers. It was through this crowdsourced archive that Sánchez-Lavega, together with amateur observers Trevor Barry and Jean-Paul Oger, first spotted a subtle wavy band circling the southern pole in 2024. Follow-up images gathered from telescopes on the ground throughout 2025 strengthened the case that something genuinely new and geometric was forming.
Ground-based telescopes, however, are limited by the blurring effects of Earth's atmosphere, and Saturn's south pole never sits at an especially convenient viewing angle. To confirm what the community suspected and to study it in real detail, the team turned to Hubble, whose position above the atmosphere and long observational history of the outer planets made it uniquely equipped to settle the question. Sánchez-Lavega has noted that scientists had, in fact, been quietly checking Hubble archives for a southern counterpart to the hexagon since 1990, precisely because of Saturn's north-south jet stream symmetry — and had come up empty every time, including throughout Cassini's long residency in the Saturn system. The Hubble data assembled for this study finally confirmed that the decagon has genuinely been present since at least 2023, ruling out the possibility that it was simply an old feature nobody had bothered to look for.
Reading Saturn's Atmosphere by the Color of Light
Part of what allowed scientists to say anything meaningful about the decagon's structure — not just its outline, but its depth — comes down to a technique astronomers frequently use with Hubble's Wide Field Camera 3: imaging the same target through several narrow filters, each sensitive to a slightly different wavelength of light. Because different wavelengths penetrate to different depths in a gas giant's hazy, layered atmosphere, comparing images taken through several filters effectively lets scientists build a rough three-dimensional picture of a feature using two-dimensional snapshots.
Applying this method to Saturn's south pole revealed that the decagon is not merely a surface marking on the tops of the clouds. Its apparent position shifts slightly depending on which wavelength is used to observe it, and researchers interpret this shift as evidence that the wave extends through multiple layers of Saturn's atmosphere rather than existing at a single altitude. In other words, the decagon isn't painted onto the planet — it's a structure with real vertical extent, embedded deep within one of Saturn's fast, powerful jet streams. In the single-filter images released alongside the color composite, the ten-sided outline is rendered with striking, almost engineered precision, a stark polygon carved into an otherwise softly banded, tan-and-orange polar landscape. Small gaps near the very center of these images, marked with an "X" inside a dashed circle, simply denote a small region where Hubble's imaging did not capture data — not a physical feature of the planet itself.
An Old Question About Why Giant Planets Draw Straight Lines
Saturn's hexagon has puzzled scientists for over 40 years primarily because straight-edged, polygonal patterns are not something intuition expects from a fluid, ever-churning atmosphere. Fluids tend to swirl, curve, and blend; they don't normally organize themselves into crisp geometric shapes with sharp vertices. Yet laboratory experiments using rotating tanks of fluid have shown that under the right conditions — specifically, a fast-moving jet stream circling a slower-moving polar vortex — instabilities in the flow can naturally organize themselves into a wave with a small number of repeating lobes, producing exactly this kind of polygonal appearance. The northern hexagon has long served as the best real-world validation of that theory.
The decagon complicates and enriches that picture. If Saturn's atmosphere can spontaneously generate a six-sided wave in one hemisphere and, apparently independently, a ten-sided wave in the other, that suggests the underlying physics is more flexible — and possibly more sensitive to specific, changeable local conditions — than previously assumed. Researchers have floated the possibility that nearby storm activity or subtle differences in the jet stream's speed and width could nudge such a wave toward forming with a different number of sides. Sánchez-Lavega has even worked out a mathematical shallow-water model demonstrating how a ten-sided pattern could plausibly emerge from turbulent flow, echoing similar modeling that helped explain the hexagon decades ago. Even so, key mysteries remain unresolved, including exactly what gives the feature its bluish tint at certain wavelengths, what those winds — estimated to be moving at roughly 400 kilometers per hour, or about 250 miles per hour — are actually made of at depth, and how far down into Saturn's atmosphere the wave truly extends.
What Happens Next
For now, scientists are approaching the decagon with more questions than answers, and that is precisely the point of NASA's long-running OPAL program, which was never designed to capture single dramatic snapshots but rather to build up a multi-year, sometimes multi-decade record of how the outer planets' atmospheres change. Mike Wong, an OPAL co-investigator at the University of California, Berkeley, has pointed out that many of the program's most significant findings only became visible after comparing years' worth of accumulated images rather than any single observation — a philosophy that this discovery exemplifies almost perfectly. Had astronomers only glanced at Saturn's south pole once, in a single year, the decagon might have looked like an unremarkable ripple rather than the leading edge of a genuinely new atmospheric structure.
Researchers now plan continued observations using both Hubble and NASA's James Webb Space Telescope, whose infrared instruments are well suited to probing deeper atmospheric layers than Hubble's optical filters can reach. Combined with improved computer modeling, these future observations aim to determine whether the decagon is a fleeting, transitional oddity that will fade as Saturn's seasons continue to shift, or whether it is settling in for the long haul, on track to become as permanent and iconic a fixture of the southern hemisphere as the hexagon has been in the north. Either outcome would be scientifically valuable: a short-lived decagon would reveal what conditions are needed to destabilize such a wave, while a long-lived one would offer a rare second data point for understanding how and why giant planets sometimes lock their atmospheres into rigid geometric patterns.
There's a broader resonance here too. Jet streams, polar vortices, and large-scale wave patterns aren't unique to Saturn — they show up, in less extreme forms, in the atmospheres of Jupiter, Uranus, Neptune, and even Earth, where the polar vortex and jet stream dynamics increasingly make headlines in the context of winter weather extremes. Untangling why Saturn's atmosphere organizes itself into hexagons in one place and decagons in another could, in a roundabout way, sharpen scientists' understanding of the fluid dynamics that govern planetary atmospheres more generally — including, ultimately, our own.
For now, the newest portrait of Saturn — a ringed globe glowing in pale yellows and oranges, its south pole ringed by an improbable ten-sided wave — stands as a reminder that even a planet studied continuously for more than 40 years can still spring a genuine surprise, if you know to keep watching, and if enough people around the world keep pointing their telescopes at the sky.
Frequently Asked Questions
1. What exactly is the "decagon" that Hubble found on Saturn? It's a giant, ten-sided atmospheric wave discovered circling Saturn's south pole at around 63 degrees south latitude. It sits inside one of Saturn's fast jet streams and extends through multiple layers of the atmosphere, making it a genuine three-dimensional structure rather than a surface marking.
2. How is the decagon different from Saturn's famous northern hexagon? The hexagon has been observed continuously for more than 40 years and appears essentially permanent, while the decagon seems to be a brand-new feature that only started emerging around 2023. It also has one more side, and scientists aren't yet sure whether it will stabilize into a long-lived pattern or fade away.
3. Who first noticed the decagon, and how? Ground-based and amateur astronomers, including Agustín Sánchez-Lavega, Trevor Barry, and Jean-Paul Oger, first spotted a subtle undulating band near Saturn's south pole in images submitted to a crowdsourced observing archive in 2024. Hubble's sharper, space-based imagery then confirmed and detailed the feature.
4. Why wasn't the decagon seen earlier, by Cassini or earlier Hubble images? Saturn's slow, decades-long seasonal cycle only recently brought its southern hemisphere into a favorable viewing position from Earth. Cassini's images from 2004–2017 showed no such pattern, and Hubble archives dating back to 1990 were also clear, suggesting the decagon is a genuinely recent development rather than something previously overlooked.
5. What will scientists study next? Researchers plan to keep observing the decagon with Hubble and the James Webb Space Telescope, along with computer modeling, to determine what is driving it, how deep into Saturn's atmosphere it extends, and whether it will become as stable and long-lasting as the northern hexagon.
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