A research team has successfully created the first-ever three-dimensional map of Uranus’s upper atmosphere. This reveals how the ice giant’s unusual magnetic field shapes spectacular auroras high above the planet’s clouds.
The team led by Paola Tiranti observed Uranus for nearly a full rotation, detecting the faint glow from molecules up to 3,100 miles (5,000 kilometres) above the cloud tops.
The observations provide the most detailed picture yet of where the planet’s auroras form and how energy moves through its atmosphere.
Auroras occur when energetic particles become trapped in a planet’s magnetic field and strike the upper atmosphere, releasing energy that creates a signature glow.
The team found that the temperatures peak between 3,000 and 4,000 kilometres above the cloud tops, whilst ion densities reach their maximum around 1,000 kilometres.
The team confirms that Uranus’ upper atmosphere has continued to cool over the past thirty years – a trend that has been surprising scientists for over three decades.
Using Webb’s Near-Infrared Spectrograph, the team mapped out the temperature and density of ions in Uranus’s ionosphere, a region where the atmosphere becomes ionised and interacts strongly with the planet’s magnetic field.
For first time, researchers were able to see Uranus’s upper atmosphere in three dimensions
“This is the first time we’ve been able to see Uranus’s upper atmosphere in three dimensions. With Webb’s sensitivity, we can trace how energy moves upward through the planet’s atmosphere and even see the influence of its lopsided magnetic field,” said lead author Paola Tiranti.
Uranus’ magnetosphere is one of the strangest in the Solar System. Unlike Earth, where the magnetic field is relatively aligned with the planet’s rotation axis, Uranus’s magnetic field is tilted by nearly 60 degrees and offset from the planet’s centre. This means its auroras sweep across the surface in complex ways, according to researchers.
Webb observations detected two bright auroral bands
The Webb observations detected two bright auroral bands near Uranus’s magnetic poles, together with a distinct depletion in emission and ion density between them – a feature likely linked to how magnetic field lines guide charged particles through the atmosphere. Similar darkened regions have been seen at Jupiter, where magnetic field geometry controls particle flow, according to a press release.
“By revealing Uranus’s vertical structure in such detail, Webb is helping us understand the energy balance of the ice giants. This is a crucial step towards characterising giant planets beyond our Solar System,” said Tiranti.
Published in Geophysical Research Letters, the study offers new insights into Uranus’s upper atmosphere, confirm its long-term cooling trend and provide key constraints for ice giant ionospheric and magnetospheric modeling.
The team revealed that the study is based on data from JWST General Observer programme 5073, led by Dr Henrik Melin of Northumbria University, which used the telescope’s Integral Field Unit on 19 January 2025 to observe Uranus for 15 hours.