Astronomers have successfully mapped the vertical structure of Uranus’ ionosphere for the very first time, uncovering unexpected temperature peaks, a decline in ion density, and enigmatic dark regions influenced by the planet’s unique magnetic field. These groundbreaking findings, achieved through nearly a full day of observations using the NIRSpec instrument aboard NASA/ESA/CSA’s James Webb Space Telescope, confirm a decades-long cooling trend in Uranus’ upper atmosphere and offer an unprecedented look at how this ice giant interacts with its surrounding space differently than other celestial bodies in our solar system.

Uranus’s upper atmosphere remains one of the least understood components in our solar system, despite its critical role in elucidating the interactions between the giant planet and its space environment.

Astronomer Paola Tiranti from Northumbria University and her team dedicated nearly an entire day to observing Uranus with Webb’s NIRSpec instrument.

They successfully measured the vertical structure of the ionosphere, the electrically charged layer of the atmosphere where auroras occur.

“This is the first time we’ve been able to visualize Uranus’s upper atmosphere in three dimensions,” Tiranti remarked.

“Utilizing Webb’s sensitivity, we can investigate how energy migrates upward through the planet’s atmosphere, even observing the effects of polarized magnetic fields.”

Measurements revealed temperature peaks at approximately 3,000 to 4,000 km above the surface, while ion density peaked around 1,000 km, significantly weaker than previously modeled predictions.

Webb also identified two bright bands of auroral emission located near Uranus’s magnetic poles, along with an unexpected area of depleted emission and density, likely tied to the planet’s unusual magnetic field geometry.

These discoveries confirm a long-term cooling trend in Uranus’ upper atmosphere and highlight new structures shaped by its magnetic environment.

These findings offer critical benchmarks for future missions and enhance our comprehension of how giant planets—both within and beyond our solar system—maintain the energy balance in their upper atmospheres.

“Uranus’ magnetosphere is one of the most peculiar in the solar system,” Tiranti emphasized.

“Its tilt and offset from the planet’s rotational axis cause its auroras to be distributed in a complex fashion across the surface.”

“Webb has provided insights into how deeply these effects penetrate into the atmosphere.”

“By detailing Uranus’s vertical structure so thoroughly, Webb aids in our understanding of the energy balance of the ice giant.”

“This represents a significant step toward characterizing giant planets beyond our solar system.”

For further details, refer to the results published in the journal Geophysical Research Letters.

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Paola I. Tiranti et al. 2026. JWST uncovers the vertical structure of Uranus’ ionosphere. Geophysical Research Letters 53 (4): e2025GL119304; doi: 10.1029/2025GL119304