Astronomers using the NASA/ESA James Webb Space Telescope have detected a series of dark, bead-like and asymmetric star-shaped features in the ionosphere and stratosphere of Saturn.
Detections of near-infrared emissions in Saturn’s ionosphere (left) show dark bead-like features embedded within bright aurora; in the stratosphere (right), 500 km below, a lopsided star-pattern extends towards the equator. Image credit: NASA / ESA / CSA / Webb / Stallard et al.
“This opportunity to use Webb was the first time we have ever been able to make such detailed near-infrared observations of Saturn’s aurora and upper atmosphere. The results came as a complete surprise,” said Northumbria University’s Professor Tom Stallard.
“We anticipated seeing emissions in broad bands at the various levels.”
“Instead, we’ve seen fine-scaled patterns of beads and stars that, despite being separated by huge distances in altitude, may somehow be interconnected — and may also be linked to the famous hexagon deeper in Saturn’s clouds.”
“These features were completely unexpected and, at present, are completely unexplained.”
The researchers focused on detecting infrared emissions by a positively charged molecular form of hydrogen, H3+, which plays a key role in reactions in Saturn’s atmosphere and so can provide valuable insights into the chemical and physical processes at work.
Webb’s Near Infrared Spectrograph allowed the scientists to simultaneously observe H3+ ions from the ionosphere, 1,100 km above Saturn’s nominal surface, and methane molecules in the underlying stratosphere, at an altitude of 600 km.
In the electrically charged plasma of the ionosphere, they observed a series of dark, bead-like features embedded in bright auroral halos.
These structures remained stable over hours but appeared to drift slowly over longer periods.
Around 500 km lower, in Saturn’s stratosphere, the team discovered an asymmetric star-shaped feature.
This unusual structure extended out from Saturn’s north pole towards the equator.
Only four of the star’s six arms were visible, with two mysteriously missing, creating a lopsided pattern.
“Saturn’s upper atmosphere has proven incredibly difficult to study with missions and telescope facilities to date due to the extremely weak emissions from this region,” Professor Stallard said.
“Webb’s incredible sensitivity has revolutionized our ability to observe these atmospheric layers, revealing structures that are completely unlike anything we’ve seen before on any planet.”
The authors mapped the exact locations of the features and found that they overlaid the same region of Saturn at different levels, with the star’s arms appearing to emanate from positions directly above the points of the storm-cloud-level hexagon.
This suggests that the processes that are driving the patterns may influence a column stretching right through Saturn’s atmosphere.
“We think that the dark beads may result from complex interactions between Saturn’s magnetosphere and its rotating atmosphere, potentially providing new insights into the energy exchange that drives Saturn’s aurora,” Professor Stallard said.
“The asymmetric star pattern suggests previously unknown atmospheric processes operating in Saturn’s stratosphere, possibly linked to the hexagonal storm pattern observed deeper in Saturn’s atmosphere.”
“Tantalizingly, the darkest beads in the ionosphere appear to line up with the strongest star-arm in the stratosphere, but it’s not clear at this point whether they are actually linked or whether it’s just a coincidence.”
While both features could have significant implications for understanding atmospheric dynamics on gas giant planets, more work is needed to provide explanations for the underlying causes.
The team hopes that additional time may be granted in future to carry out follow-up observations of Saturn with Webb to further explore the features.
With the planet at its equinox, which occurs approximately every 15 Earth years, the structures may change dramatically as Saturn’s orientation to the Sun shifts and the northern hemisphere moves into autumn.
“Since neither atmospheric layer can be observed using ground-based telescopes, the need for follow-up Webb observations during this key time of seasonal change on Saturn is pressing,” said Professor Stallard, lead author of a paper published in the journal Geophysical Research Letters.
The authors also presented the results this month at the EPSC-DPS2025 Joint Meeting in Helsinki, Finland.
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Tom S. Stallard et al. 2025. JWST/NIRSpec Detection of Complex Structures in Saturn’s Sub-Auroral Ionosphere and Stratosphere. Geophysical Research Letters 52 (17): e2025GL116491; doi: 10.1029/2025GL116491
Tom S. Stallard et al. 2025. JWST’s transformational observations of Giant Planet ionospheres. EPSC Abstracts 18: EPSC-DPS2025-817; doi: 10.5194/epsc-dps2025-1438