Webb Telescope Provides First 3D Map of Uranus’s Upper Atmosphere
For the first time, astronomers have mapped the vertical structure of Uranus’s upper atmosphere, revealing how temperature and electrically charged particles change with altitude across the planet. An international research team, utilizing the data from the James Webb Space Telescope (JWST) and its Near-Infrared Spectrograph (NIRSpec) instrument, observed Uranus for nearly a full rotation. This observation, conducted on , allowed scientists to capture faint molecular emissions high above the cloud tops, providing new insight into how ice giant planets manage energy in their upper layers.
The study, led by Paola Tiranti of Northumbria University in the United Kingdom, measured temperatures and ion densities extending up to kilometers above Uranus’s visible clouds. This region, known as the ionosphere, is where the atmosphere becomes ionized and strongly interacts with the planet’s magnetic field. The findings were published in the journal Geophysical Research Letters.
Unprecedented Detail of Uranus’s Auroras
These observations provide the clearest picture yet of where Uranus’s auroras take shape and how its unusually tilted magnetic field affects them. The data also confirm a continuing trend: Uranus’s upper atmosphere has been cooling for the past three decades. Temperatures peak between and kilometers above the clouds, while ion densities reach their maximum closer to kilometers. The results also reveal longitudinal variations, linked to the complex geometry of the planet’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.”
Continuing Cooling Trend and Atmospheric Temperature
The new measurements confirm that Uranus’s upper atmosphere continues to cool, a pattern first identified in the early 1990s. Researchers calculated an average temperature of approximately kelvins (about degrees Celsius), which is lower than previous readings obtained from ground-based observatories and earlier spacecraft missions.
A Unique Magnetosphere and Auroral Bands
Webb’s observations also shed light on Uranus’s peculiar magnetosphere. The planet’s rotation axis is tilted over degrees, causing it to rotate on its side. The magnetic axis is tilted nearly degrees away from its rotation axis. This creates a highly variable magnetosphere, resulting in auroras that sweep across the surface in complex patterns.
The telescope detected two bright auroral bands near the planet’s magnetic poles. Notably, the team found a region between these bands with reduced emissions and fewer ions, likely due to the way magnetic field lines guide charged particles through the atmosphere. Similar features have been observed on Jupiter.
“Uranus’s magnetosphere is one of the strangest in the Solar System,” added Tiranti. “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. By revealing Uranus’s vertical structure in such detail, Webb is helping us understand the energy balance of the ice giants. This is a crucial step towards characterizing giant planets beyond our Solar System.”
Webb Telescope and International Collaboration
The findings are based on data collected through JWST General Observer program (Principal Investigator: H. Melin of Northumbria University in the United Kingdom). The observation utilized NIRSpec’s Integral Field Unit to continuously monitor Uranus for approximately hours.
The James Webb Space Telescope represents a significant international collaboration between NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA). ESA provided the launch service using the Ariane 5 rocket, oversaw mission modifications, and secured launch services through Arianespace. ESA also supplied the NIRSpec instrument and contributed percent of the mid-infrared instrument (MIRI), developed by a consortium of European Institutes in partnership with JPL and the University of Arizona.
