Temperature Anomalies and Cooling

The measurements show that temperatures peak between 3,000 and 4,000 km, while ion densities reach their maximum around 1,000 km. Data from the NIRSpec instrument confirmed that Uranus’s upper atmosphere is still cooling—a trend that began in the early 1990s. The team measured an average temperature of around 426 kelvins (about 150 °C), lower than previous records.

Study Details

• Instrument: JWST (NIRSpec Integral Field Unit)
• Observation Time: 15 hours (nearly a full planetary rotation)
• Publication: Geophysical Research Letters

Tilted Magnetic Field and Auroras

Uranus’s magnetosphere is one of the strangest in the Solar System—highly tilted and offset from its rotation axis. Webb detected two bright auroral bands near the magnetic poles, separated by a distinct depletion in ion density. Similar darkened regions are seen at Jupiter, where the magnetic field geometry strictly controls charged particle movement.

"With Webb’s sensitivity, we can trace how energy moves upward through the planet’s atmosphere. By revealing Uranus’s vertical structure in such detail, Webb is helping us understand the energy balance of the ice giants—a crucial step towards characterising exoplanets," said Paola Tiranti, lead author (Northumbria University).

Read more in the official ESA press release.

Credit: ESA