The James Webb Space Telescope delivered two striking discoveries in quick succession this month: the first three-dimensional map of Uranus's upper atmosphere and auroras, and detailed new infrared portraits of a little-known nebula that looks like a brain floating inside a transparent skull.
A New View of Uranus's Auroras
An international team led by Paola Tiranti, a PhD student at Northumbria University in England, used Webb's Near-Infrared Spectrograph (NIRSpec) to observe Uranus for 15 hours — nearly a full rotation of the planet — on January 19, 2025. The resulting data, published February 19 in Geophysical Research Letters, allowed scientists for the first time to map the temperature and density of ions stretching up to 5,000 kilometers above the planet's cloud tops.
The observations revealed two bright auroral bands near Uranus's magnetic poles, along with a distinct low-emission zone between them likely shaped by the planet's magnetic field lines. While the Hubble Space Telescope first captured images of auroras on Uranus in 2011, Webb's data represent the most detailed picture yet of how those auroras form and how the planet's tilted magnetic field influences them.
"This is the first time we've been able to see Uranus's upper atmosphere in three dimensions," Tiranti said in a statement released by the European Space Agency. "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 team also confirmed that Uranus's upper atmosphere continues to cool, a trend first observed in the early 1990s. Webb measured an average temperature of about 426 kelvins — roughly 150 degrees Celsius — lower than values recorded by ground-based telescopes or the Voyager 2 spacecraft, which performed the only close flyby of Uranus in 1986.
The "Exposed Cranium" Nebula
On February 25, NASA and ESA released Webb's new infrared images of nebula PMR 1, nicknamed the "Exposed Cranium" for its resemblance to a brain inside a translucent skull. The nebula is being created by an aging star shedding its outer layers, and Webb captured its features using both its NIRCam and MIRI instruments.
The images reveal distinct phases of the star's evolution — an outer shell of hydrogen blown off first, and a more structured inner cloud containing heavier gases. A dark lane running vertically through the nebula gives it the look of left and right brain hemispheres and may be linked to twin jets of material erupting from the central star. NASA's now-retired Spitzer Space Telescope first glimpsed the nebula in infrared more than a decade ago, but Webb's resolution has exposed detail that Spitzer could not resolve.
What Comes Next
Scientists say much remains unknown about PMR 1, including whether the dying star at its center is massive enough to end in a supernova or will instead cool into a dense white dwarf. As for Uranus, upcoming Webb observation cycles will monitor seasonal changes as the planet's north pole tilts toward the sun, with peak summer expected around 2028 to 2030. "By revealing Uranus's vertical structure in such detail, Webb is helping us understand the energy balance of the ice giants," Tiranti said. "This is a crucial step towards characterizing giant planets beyond our solar system."
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