For the first time, an international team of astronomers have mapped the vertical structure of Uranus’s upper atmosphere, uncovering how temperature and charged particles vary with height across the planet. Using Webb’s NIRSpec instrument, the team observed Uranus for nearly a full rotation, detecting the faint glow from molecules high above the clouds.

These unique data provide the most detailed portrait yet of where the planet’s auroras form, how they are influenced by its unusually tilted magnetic field, and how Uranus’s atmosphere has continued to cool over the past three decades. The results, published in Geophysical Research Letters, offer a new window into how ice-giant planets distribute energy in their upper layers.

Led by Paola Tiranti of Northumbria University in the United Kingdom, the study mapped out the temperature and density of ions in the atmosphere extending up to 5,000 kilometers above Uranus’s cloud tops, a region called the ionosphere where the atmosphere becomes ionized and interacts strongly with the planet’s magnetic field. The measurements show that temperatures peak between 3,000 and 4,000 kilometers, while ion densities reach their maximum around 1,000 kilometers, revealing clear longitudinal variations linked to the complex geometry of the magnetic field.