"This opportunity to use JWST 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," Stallard explained.
Researchers expected to find broad atmospheric emissions but instead discovered fine-scale structures. In Saturn's ionosphere, 1,100 kilometers above its nominal surface, they observed a chain of dark, bead-like patterns embedded within bright auroral halos. These beads persisted over hours, drifting slowly across the sky.
Roughly 500 kilometers below, in the stratosphere, the team detected a lopsided star-shaped feature stretching outward from the planet's north pole. Only four of the expected six arms were visible, producing an asymmetry that remains unexplained.
"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," said Stallard. "JWST's incredible sensitivity has revolutionised our ability to observe these atmospheric layers, revealing structures that are completely unlike anything we've seen before on any planet."
The researchers mapped the features and found that they overlay the same geographic region of Saturn at different altitudes, with the star's arms radiating from points above the planet's hexagonal storm deep in the cloud tops. This alignment hints at vertical processes linking the ionosphere and stratosphere.
The dark beads may be tied to interactions between Saturn's magnetosphere and its rotating atmosphere, shedding light on auroral dynamics. The distorted star pattern could signal new processes in the stratosphere, potentially linked to the iconic hexagon. Intriguingly, the darkest beads appear to align with the strongest arm of the star, though whether this is causal or coincidental is unknown.
The discoveries raise important questions about energy transport and atmospheric dynamics on gas giants. Further JWST observations are planned, particularly as Saturn approaches its equinox, when changing sunlight could transform these atmospheric structures.
Research Report:JWST/NIRSpec detection of complex structures in Saturn's sub-auroral ionosphere and stratosphere
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