Astronomers have, for the first time, created a three-dimensional map of the upper atmosphere of Uranus, revealing new details about the ice giant’s auroras, temperature variations, and ongoing atmospheric cooling. The breakthrough, achieved using the James Webb Space Telescope (JWST), provides a unique window into the energy distribution within Uranus’s upper layers and sheds light on the planet’s unusual magnetic field.
The research team, led by Paola Tiranti of Northumbria University in the United Kingdom, observed Uranus for nearly a full rotation using JWST’s Near-Infrared Spectrograph (NIRSpec). This allowed them to detect the faint glow emitted by molecules high above the planet’s cloud tops, extending up to 5,000 kilometers (3,100 miles). The resulting data offers the most detailed portrait yet of the region known as the ionosphere, where the atmosphere becomes ionized and interacts strongly with the planet’s magnetic field.
Understanding Uranus’s Atmospheric Structure
The team mapped the temperature and density of ions within the ionosphere, revealing that temperatures peak between 3,000 and 4,000 kilometers (1,860 and 2,485 miles) above the cloud tops. Ion densities, meanwhile, reach their maximum around 1,000 kilometers (620 miles). These measurements demonstrate clear variations in altitude, linked to the complex geometry of Uranus’s magnetic field.
“This is the first time we’ve been able to see Uranus’s upper atmosphere in three dimensions,” said Tiranti. “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.”
The data also confirms a long-observed trend: Uranus’s upper atmosphere continues to cool. Measurements taken by JWST show an average temperature of around 426 kelvins (approximately 150 degrees Celsius or 300 degrees Fahrenheit), lower than previous measurements recorded by ground-based telescopes or earlier spacecraft missions. This cooling trend has been ongoing since the early 1990s, and the new observations provide further evidence of this phenomenon.
Auroral Displays and the Magnetic Field
JWST also detected two distinct bands of bright auroras near Uranus’s magnetic poles. These auroras are created when energetic particles become trapped in the planet’s magnetic field and collide with the upper atmosphere, releasing energy in the form of light. The observations revealed a region of reduced emission and ion density between the two auroral bands, a characteristic linked to the unique configuration of Uranus’s magnetic field.
Uranus’s magnetic field is notably unusual. It is tilted and offset from the planet’s rotational axis, causing its auroras to sweep across the surface in complex patterns. The JWST data provides insights into how these magnetic field characteristics influence the planet’s atmospheric dynamics.
“Uranus’s magnetosphere is one of the strangest in the Solar System,” Tiranti explained. “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.”
Implications for Ice Giant Research
The findings from this study have significant implications for our understanding of ice giant planets, both within our solar system and beyond. By revealing the vertical structure of Uranus’s atmosphere in such detail, JWST is helping scientists understand how energy is balanced within these types of planets.
“By revealing Uranus’s vertical structure in such detail, Webb is helping us understand the energy balance of the ice giants,” Tiranti stated. “This is a crucial step towards characterizing giant planets beyond our Solar System.”
The research, published on , in Geophysical Research Letters, marks a significant advancement in planetary science and highlights the capabilities of the James Webb Space Telescope for studying the atmospheres of distant worlds.
