40-year mystery of inexplicably strong radiation on Uranus may finally be solved
Scientists may have solved a long-standing mystery surrounding Uranus’ extraordinarily powerful radiation belt.
A new analysis of Voyager 2 data suggests that a temporary space weather event may have made the planet’s electron radiation belt more intense than usual, as Voyager 2 passed by. These results could help explain why the radiation belt was so much more powerful than scientists had predicted.
In January 1986, Voyager 2 flew by Uranus and measured the strength of its radiation belts. While the ion radiation belt was a little weaker than expected, the electron radiation belt was much more intense than scientists had predicted – close to the maximum intensity Uranus could withstand. Since then, scientists have been trying to understand how and why this happened.
“Science has come a long way since Voyager 2’s flyby,” Robert Allenspace physicist at the Southwest Research Institute (SwRI) and co-author of the new research, said in a statement. statement. “We decided to take a comparative approach by looking at the Voyager 2 data and comparing it to the Earth observations we have made over the decades since.”
Earth versus Uranus
In the study, published in November 2025 in the journal Geophysical research lettersAllen and his colleagues revisited data collected by Voyager 2 during its flyby of Uranus. They found several similarities between Voyager data and data collected from Earth orbit during a 2019 space weather event.
The team discovered that Uranus’ unusually intense radiation belt may have been caused by a “co-rotating interaction region.” A co-rotating interaction region occurs when high-speed solar winds exceed slower solar wind fluxes. The phenomenon could have accelerated the electrons and added energy to the radiation belt, the researchers said.
“In 2019, Earth experienced one of these events, which caused an immense electronic acceleration of electrons in the radiation belt,” said the study co-author. Sarah Vinesspace physicist at SwRI. “If a similar mechanism interacted with the Uranian system, it would explain why Voyager 2 saw all this unexpected extra energy.”
If so, this raises many other questions about the physics of Uranus’ magnetosphere and its interactions with the solar wind, including the stability of the radiation belt during extreme seasons caused by the tilt of the planet’s rotation axis. A spacecraft orbiting Uranus and collecting data from different parts of the magnetosphere could help answer these questions, the researchers wrote in the study.
“This is just one more reason to send a mission targeting Uranus,” Allen said in the statement. “These findings have important implications for similar systems, such as Neptune.”
Allen, RC, Vines, SK and Ho, GC (2025). Solving the mystery of Uranus’ electron radiation belt: leveraging knowledge of Earth’s radiation belts in a re-examination of Voyager 2 observations. Geophysical research letters52(22). https://doi.org/10.1029/2025gl119311
