Led by Paola Tiranti from Northumbria University, a research team has made groundbreaking observations of Uranus using the James Webb Space Telescope (JWST). They focused on the planet's ionosphere, a region extending up to 5000 km above the visible cloud layer, where temperatures and ion densities are significantly influenced by Uranus's magnetic field.
This research provides an unprecedented view of Uranus's auroras and illustrates how its uniquely tilted magnetic field impacts them. Over the last three decades, Uranus's upper atmosphere has shown signs of cooling, with peak temperatures recorded between 3000 and 4000 km above the clouds, and ion densities peaking around 1000 km. The findings indicate notable variations in measurements based on longitude, reflecting the intricate structure of the planet's magnetic field.
"For the first time, we are observing Uranus's upper atmosphere in three dimensions," stated Paola. "Webb's advanced sensitivity allows us to track energy movements within the atmosphere and to see the effects of its irregular magnetic field."
Continuing Cooling Trend of Uranus
The latest data confirm that Uranus's upper atmosphere is still cooling, a trend first recognized in the early 1990s. Researchers reported an average temperature of approximately 426 kelvins (around 150 degrees Celsius), which is notably lower than previous measurements from ground-based observatories and earlier missions.
Bright Auroras and a Unique Magnetosphere
The JWST has identified two prominent auroral bands close to Uranus's magnetic poles. Between these bands lies a region with diminished emissions and fewer ions, likely related to shifts in magnetic field lines. Similar dark areas have been observed on Jupiter, where the magnetic field's configuration directs charged particles through the upper atmosphere.
"Uranus's magnetosphere is among the most peculiar in our Solar System," Paola remarked. "Its tilt and offset from the planet's rotational axis cause its auroras to traverse the surface in intricate patterns. Webb has unveiled how these phenomena extend deep into the atmosphere. By elucidating Uranus's vertical structure in such detail, Webb is enhancing our understanding of the energy dynamics of ice giants, a vital step toward characterizing exoplanets beyond our Solar System."
Research Insights and the Webb Mission
The study's findings stem from JWST General Observer program 5073, led by H. Melin of Northumbria University. On January 19, 2025, the team conducted a continuous 15-hour observation of Uranus using the NIRSpec's Integral Field Unit. The results were published in the journal Geophysical Research Letters.
The James Webb Space Telescope, the most advanced space telescope ever launched, is a collaborative effort between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). ESA played a crucial role in the launch and modification processes, providing the NIRSpec instrument and contributing significantly to the mid-infrared instrument MIRI.