Overview
- An international team led by Paola Tiranti used JWST’s NIRSpec to track faint ionospheric emission through nearly a full Uranian rotation, mapping up to about 5,000 kilometers above the cloud tops.
- Temperatures peak between roughly 3,000 and 4,000 kilometers in altitude, while ion densities maximize near 1,000 kilometers, with clear longitudinal variations tied to magnetic geometry.
- Webb identified two bright auroral bands near the magnetic poles and a depleted zone of emission and ion density between them, a feature consistent with transitions in magnetic field lines.
- The measurements confirm a continued cooling of the upper atmosphere since the early 1990s, with an average temperature near 426 kelvins that is lower than previous ground or spacecraft readings.
- The results, drawn from GO program 5073 using NIRSpec’s Integral Field Unit on January 19, 2025, refine ice-giant energy balance models and offer benchmarks for interpreting giant exoplanet atmospheres.