Webb Telescope Maps Uranus Atmosphere
NASA's James Webb Space Telescope produced the first 3D map of Uranus's upper atmosphere, revealing temperatures of 426 Kelvin — 150°C cooler than 1990s measurements. The planet's tilted magnetic field (60 degrees off rotational axis) creates unique aurora patterns. This cooling trend suggests major atmospheric changes tied to orbital cycles or solar activity.
The 3D map was created using the James Webb Space Telescope's Near InfraRed Spectrograph (NIRSpec), which observed the ice giant for nearly a full rotation—a day on Uranus is about 17 hours. A team led by Paola Tiranti of Northumbria University in the U.K. mapped the ionosphere, a charged layer extending up to 5,000 km above the planet's cloud tops. This cooling trend has been a long-standing mystery. While initially thought to be linked to the Sun's 11-year cycle, scientists now believe the cause is a decades-long decline in the solar wind's outward pressure. This reduced pressure allows Uranus's protective magnetic bubble, or magnetosphere, to expand, which in turn affects energy flow and cools the upper atmosphere. Webb's observations revealed that temperatures in the upper atmosphere peak between 3,000 and 4,000 kilometers in altitude. The density of ions, however, is greatest at a much lower altitude of around 1,000 kilometers. The planet's lopsided magnetic field means its auroras, which glow mainly in infrared and ultraviolet light, sweep across the surface in complex ways rather than remaining near the poles like on Earth. The telescope identified two bright auroral bands near the magnetic poles, along with darkened regions between them, a feature also seen on Jupiter. Before this, the only up-close data came from Voyager 2's brief flyby on January 24, 1986. That mission first measured the unexpectedly hot thermosphere, creating a puzzle known as the "giant planet energy crisis," as the heat source couldn't be explained by solar radiation alone. Looking ahead, a dedicated Uranus Orbiter and Probe has been named the highest-priority future flagship mission by U.S. planetary scientists. If approved, the mission could launch as early as 2031 and would deploy an atmospheric probe to take direct measurements of the ice giant's atmosphere.
