19/02/2026
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For the first time, an international team of astronomers has mapped the vertical structure of Uranus’s upper atmosphere, revealing how temperature and charged particles change with altitude across the planet. Using the NIRSpec instrument on the NASA/ESA/CSA James Webb Space Telescope, the team observed Uranus for a nearly complete rotation, detecting faint flashes from molecules above the clouds. The results offer a new window into how ice-giant planets distribute energy in their upper layers.
Uranus Collage (January 2025)
Led by Paola Tiranti of Northumbria University in the United Kingdom, the study mapped the temperature and density of ions in the atmosphere extending 5000 km above the tops of Uranus’s clouds, a region called the ionosphere where the atmosphere becomes ionized and interacts strongly with the planet’s magnetic field. These unique data provide the most detailed picture yet of where the planet’s auroras form, how they are affected by its unusually tilted magnetic field, and how Uranus’s atmosphere has been cooling over the past three decades. Measurements show that the temperature peaks between 3000 and 4000 km, while the ion density reaches its maximum around 1000 km, revealing clear longitudinal variations associated with the complex geometry of the magnetic field.
“This is the first time we have been able to see the upper atmosphere of Uranus in three dimensions,” Paola said. “With Webb’s sensitivity, we can trace how energy moves upward through the planet’s atmosphere and even see the effects of its unbalanced magnetic field.”
Webb’s data confirms that Uranus’s upper atmosphere is still cooling, extending a trend that began in the early 1990s. The team measured an average temperature of about 426 Kelvin (about 150 degrees Celsius), which is lower than values recorded by ground-based telescopes or previous spacecraft.
Two bright auroral bands were detected near the magnetic poles of Uranus, as well as a pronounced decrease in emission and ion density in part of the region between the two bands (a feature that may be associated with the transition in magnetic field lines). Similar dark regions have been observed on Jupiter, where the geometry of the magnetic field controls how charged particles travel through the upper atmosphere.
“Uranus’ magnetosphere is one of the strangest in the solar system,” Paola said. “It is tilted and offset from the planet’s rotation axis, meaning its auroras extend across the surface in complex ways. Webb has now shown us how deep into the atmosphere those effects reach. By revealing the vertical structure of Uranus in such detail, Webb is helping us understand the energy balance of the ice giants. This is an important step toward characterizing the giant planets beyond our solar system.”
The study is based on data from JWST General Observer Program 5073 (PI: H. Mellin of Northumbria University in the United Kingdom), which used NIRSpec’s Integral Field Unit to observe Uranus for 15 hours on January 19, 2025. This research has been published in geophysical research paper.
Rotation of Uranus in timelapse
More information
Webb is the largest, most powerful telescope ever launched into space. Under an international cooperation agreement, ESA provided the launch service of the telescope using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and the procurement of the launch service by Arianespace. ESA also provided 50% of the workhorse spectrograph NIRSpec and the mid-infrared instrument MIRI, which was designed and built by a consortium of nationally funded European institutions (MIRI European Consortium) in partnership with JPL and the University of Arizona.
WEB is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).
science paper
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