James Webb Space Telescope finds strange beads and patterns in Saturn’s sky

For decades, Saturn's upper atmosphere has been one of the solar system's great enigmas. Even the Cassini spacecraft, which orbited Saturn for over a decade, had difficulty catching clear signals from the thin layers just under the bright auroras. That veil of secrecy has now been lifted by the James Webb Space Telescope, which has discovered bizarre, never-before-seen patterns in Saturn's skies.

On November 29, 2024, Webb's Near-Infrared Spectrograph looked at Saturn's north pole for nearly ten hours—a Saturnian day in full. The instrument made over 3,600 light slices of wavelengths between 2.8 and 5.2 microns, separating apart sunlight, heat, methane, and ionized hydrogen emissions. Astronomers made the most detailed maps to date of Saturn's upper atmosphere by stacking these measurements.

What they saw shocked them. The telescope picked up rotating auroral additions, bead-like structures elongated on the ionosphere, and a dark polar cap stretched out into a star-pattern in the stratosphere. None of these was anything to have been seen on Earth, Jupiter, or any other planet.

"These properties were completely unexpected and, to date, are completely unexplained," explained Tom Stallard, a planetary scientist at Northumbria University who identified the discovery at the EPSC-DPS 2025 Joint Meeting in Helsinki.

Saturn's auroras form in the same way as Earth's northern lights—when external charged particles strike the atmosphere of the planet. But what the new Webb data had uncovered was different. Rather than spontaneous brightenings which are characteristic of magnetic storms, the auroral emissions were regulated by Saturn's own rotating atmosphere first and foremost. That is, internal winds and currents of the planet were controlling the lights, rather than space weather from outside.

While that was happening, methane fluorescence in the stratosphere showed a sprawling four-armed star coming out of the north pole. Two of the arms were absent, making the design curiously lopsided. These patterns stretched all the way into Saturn's mid-latitudes, proposing dynamics that no scientist has ever tried to model.

The most enigmatic discovery was probably a trail of dark "beads" spread out over 55 to 65 degrees north. Each bead appeared as a faint pocket in bright auroral rings. A few were stable over hours, while others shifted slightly as Saturn rotated.

None of the other planets have yielded anything like that. Scientists considered a few options. The beads could be the result of turbulence as powerful winds shear against one another, creating ripples like waves at the boundary of two fluids. Such so-called Kelvin-Helmholtz instabilities could etch bead-shaped cavities in Saturn's radiating ionosphere.

"Saturn's upper atmosphere has been incredibly difficult to study with missions and telescope resources to date because the emissions there are so low," Stallard said. "JWST's incredible sensitivity has radically altered what we can see in these atmospheric layers, and what we see is completely unlike anything we've ever seen on any other planet."

Saturn is famous for its gargantuan hexagon—a gigantic six-sided jet stream that whorls about 70 degrees north. The gargantuan feature, most recently closely observed in 2017, usually appears in thermal views. In Webb's recent observations, the hexagon was faint and showed only flashes of alternating light and dark blotches.

Glowing over it, though, shone the irregular star pattern radiating from the north pole. Its arms seemed to drop loosely in accordance with points of the inner hexagon, hesitantly hinting at a relationship between the two layers. But it's not certain. "Tantalisingly, the most powerful beads in the ionosphere seem to follow the brightest star-arm in the stratosphere," said Stallard. "But it's unknown at the moment whether they are actually linked or if it's just coincidence."

The beads were tracked through more than 100 images by the researchers. One of them, designated as "alpha," gradually moved equatorward during the 10-hour interval. Others, labeled "beta" and "gamma," did not move, changing in brightness by less than 10 percent. This short-term constancy and long-term drift made the beads improbable random flashes but instead dynamically stable features.

If the origin was Saturn's icy moon Enceladus, the beads would have been found aligned in the magnetic footprint of its water vapor plumes. But no such correlation was found by the Webb observations. The beads were homegrown features of Saturn's ionosphere, not the result of some outside source.

The results were obtained by a team of 23 researchers representing the United Kingdom, United States, France, and Japan, from institutions such as Boston University, UC Berkeley, the Paris Observatory, Lancaster University, and Imperial College London. The project combined the expertise of early-career researchers with that of established scientists.

By contrasting H₃⁺ ion emissions a long way above Saturn with methane patterns hundreds of kilometers beneath, the team mapped out structures running through a column of atmosphere higher than a thousand kilometers. That vertical alignment is likely to be the reason for beads and star-arms appearing to be mirror opposites of one another, though how they form is not known.

When the Cassini spacecraft plunged into Saturn's atmosphere in 2017, it seemed that the era of high-resolution Saturn science was over. The Webb telescope has proved otherwise. From nearly a billion miles away, it can resolve structures Cassini never even glimpsed close up.

The results not only restore missing information about Saturn’s periodic currents but also reveal entirely new features. As Stallard put it, “We anticipated seeing emissions in broad bands at the various levels. Instead, we’ve seen fine-scaled patterns of beads and stars that may somehow be interconnected—and may also be linked to the famous hexagon deeper in Saturn’s clouds.”

These images provide more than cosmic eye candy. They permit scientists to experiment with models of atmospheric behavior in extreme environments. What scientists learn about Saturn's turbulence, wind shear, and chemistry could enhance forecasting of the upper atmosphere on Earth, which has unstable layers but is harder to observe directly.

It also indicates the way toward further research on Jupiter, Uranus, and Neptune. Webb has already picked up on surprise auroras on Neptune, proving its ability to find feeble signals across the outer worlds. Building on this work, researchers hope to compare atmospheric processes in several giants, gaining a better sense of how planets form.

For humanity, the biggest gain may be perspective. Every new layer peeled back on Saturn reminds us how much remains unknown. In studying strange beads and asymmetric stars on a distant gas giant, scientists sharpen the tools that one day may help predict Earth’s changing climate and uncover the secrets of exoplanets orbiting faraway suns.

Research findings are available online in the journal Geophysical Research Letters.

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