Saturn has been famous for the six-sided storm system wrapped around its north pole for more than 40 years.

Now Hubble has found something even stranger at the other end of the planet: a giant atmospheric wave with 10 sides.

The newly identified “decagon” circles Saturn’s south pole inside one of the gas giant’s ferocious jet streams. Astronomers say it appears to have strengthened over just the past few years, giving them a rare chance to watch a planetary-scale weather pattern take shape.

The discovery is visually spectacular, but the science behind it may be even more interesting.

NASA’s Hubble team announced that the pattern is the first large, regular-sided jet feature ever observed in Saturn’s southern hemisphere. Researchers traced faint hints of it in Hubble images from 2023, saw the structure become clearer in 2024, and found a distinctly ten-sided wave in 2025 observations.

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Saturn’s changing seasons helped make the discovery possible. The planet’s south pole had been difficult to observe from Earth for years, but its tilt gradually brought the region back into view.

Ground-based observers first noticed an undulating band. Hubble’s sharper images allowed the team to resolve the geometry.

The feature is not a solid object or a neat outline drawn on the clouds. It is a vast meandering wave embedded in a high-speed atmospheric jet.

Different Hubble wavelengths place the pattern at slightly different positions, evidence that it reaches through several layers of Saturn’s atmosphere.

That makes the decagon a three-dimensional weather system on an almost unimaginable scale. The pattern wraps around an entire polar region of a planet more than nine times wider than Earth, and scientists are watching it evolve in real time.

Hubble views of Saturn and the ten-sided atmospheric wave around its south pole
Hubble views of Saturn and the newly identified decagon around its south pole. Credit: NASA, ESA, STScI, Agustin Sánchez-Lavega (UPV), Amy Simon (NASA-GSFC), Michael Wong (UC Berkeley); image processing: Alyssa Pagan (STScI).

The obvious comparison is Saturn’s northern hexagon, a six-sided jet-stream pattern discovered in Voyager images from 1980 and 1981.

That northern formation has endured through every observation for more than four decades. The southern decagon is behaving differently: older Cassini images showed no similar long-lived feature, and the latest Hubble sequence suggests the 10-sided wave may have developed only recently.

“The most intriguing part to me is that this seems to have just formed recently,” NASA planetary scientist Amy Simon said. “The question is, why did it suddenly form now when we haven’t seen one before?”

The contrast gives researchers a natural experiment. One pole carries a remarkably stable hexagon; the other now holds a newer, evolving decagon.

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Comparing them may reveal why fast-moving atmospheric jets organize into geometric waves and what allows some patterns to persist for decades.

The peer-reviewed study in Science Advances identifies the southern feature as a wave with 10 vertices rather than a rigid storm wall. The authors measured it inside the jet near 60 degrees south latitude and concluded that it is vertically trapped and confined by the surrounding atmospheric flow.

The decagon itself drifts eastward far more slowly than the jet carrying it. Its corners also oscillate instead of staying fixed, another clue that astronomers are seeing a dynamic wave pattern rather than a permanent geometric structure.

Computer models can create polygonal waves under certain conditions, but the exact trigger on Saturn remains unresolved. A nearby red-colored anticyclone may influence the flow, and seasonal changes may also matter, yet current observations do not establish a single cause.

Researchers plan to keep watching with Hubble and the James Webb Space Telescope. They want to learn whether the 10 sides sharpen, weaken, change number, or settle into a stable configuration that could rival the northern hexagon’s extraordinary lifespan.

That is the beauty of this discovery: Hubble may have caught Saturn in the act of building one of the solar system’s strangest weather formations.

For a planet people have watched closely for generations, Saturn still knows how to deliver a surprise.

This is a Guest Post from our friends over at WLTReport. View the original article here.

 

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