James Webb Space Telescope captures strange magnetic forces warping Uranus

The project was led by Paola Tiranti of Northumbria University in the United Kingdom. The team measured temperatures and ion densities as far as 5000 km above the visible clouds, within a region known as the ionosphere, where the atmosphere becomes ionized and strongly influenced by the planet's magnetic field.

These observations provide the clearest picture yet of where Uranus's auroras take shape and how its unusually tilted magnetic field affects them. The data also show that the planet's upper atmosphere has continued to cool over the past thirty years. Temperatures reach their highest levels between 3000 and 4000 km above the clouds, while ion densities peak closer to 1000 km. The results also reveal clear differences with longitude, tied to the complex structure of the magnetic field.

"This is the first time we've been able to see Uranus's upper atmosphere in three dimensions," said Paola. "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."

Evidence That Uranus Is Still Cooling

The new measurements confirm that Uranus's upper atmosphere continues to cool, a pattern first identified in the early 1990s. The researchers calculated an average temperature of about 426 kelvins (about 150 degrees Celsius), which is lower than readings previously obtained from ground based observatories or earlier spacecraft missions.

Auroras and a Strangely Shaped Magnetosphere

Webb detected two bright auroral bands near the planet's magnetic poles. Between those bands, the team found an area with reduced emissions and fewer ions (a feature likely linked to transitions in magnetic field lines). Similar darker regions have been observed on Jupiter, where the shape of the magnetic field guides the motion of charged particles through the upper atmosphere.

"Uranus's magnetosphere is one of the strangest in the Solar System," added Paola. "It's tilted and offset from the planet's rotation axis, which means its auroras sweep across the surface in complex ways. Webb has now shown us how deeply those effects reach into the atmosphere. 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 characterizing giant planets beyond our Solar System."

Study Details and the Webb Mission

The findings are based on data from JWST General Observer program 5073 (PI: H. Melin of Northumbria University in the United Kingdom). On January 19, 2025, researchers used NIRSpec's Integral Field Unit to observe Uranus continuously for 15 hours. The results were published in the journal Geophysical Research Letters.

Webb is the most powerful space telescope ever launched. As part of an international collaboration, the European Space Agency provided the launch service using the Ariane 5 rocket. ESA also oversaw modifications required for the mission and secured launch services through Arianespace. In addition, ESA supplied the NIRSpec instrument and contributed 50 percent of the mid infrared instrument MIRI, which was developed by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

The James Webb Space Telescope is a joint mission of NASA, ESA and the Canadian Space Agency (CSA).