Scientists now think a major solar wind event supercharged Uranus’ radiation belts during Voyager 2’s flyby, offering a new explanation for puzzling decades-old measurements. Credit: Shutterstock

Powerful waves unleashed by solar storms could be the key to understanding extreme radiation.

Southwest Research Institute (SwRI) researchers now think they have found the answer to a puzzle that has lingered for nearly four decades involving Uranus and its unusual radiation environment.

When Voyager 2 completed its first and only visit to the planet in 1986, the spacecraft detected an unexpectedly intense electron radiation belt, far stronger than scientists had predicted. Comparisons with other worlds suggested that Uranus should not have produced such extreme values. The discovery left scientists questioning how a planet so different from the rest of the solar system could maintain such a powerful band of trapped electrons.

New investigations are offering a potential explanation. SwRI scientists propose that the conditions recorded by Voyager 2 may resemble events seen near Earth during major solar wind disturbances. Researchers now suspect that a solar wind feature known as a co-rotating interaction region was moving through the Uranian system at the time of the flyby. If so, this passing structure could account for the unusually high energy levels Voyager 2 measured.

SwRI scientists compared space weather impacts of a fast solar wind structure (first panel) driving an intense solar storm at Earth in 2019 (second panel) with conditions observed at Uranus by Voyager 2 in 1986 (third panel) to potentially solve a 39-year-old mystery about the extreme radiation belts found. The ‘chorus’ wave is a type of electromagnetic emission that may accelerate electrons and could have resulted from the solar storm. Credit: Southwest Research Institute

“Science has come a long way since the Voyager 2 flyby,” said SwRI’s Dr. Robert Allen, lead author of a paper outlining this research. “We decided to take a comparative approach looking at the Voyager 2 data and compare it to Earth observations we’ve made in the decades since.”

Extreme Space Weather at Uranus

This new study indicates that the Uranian system may have experienced a space weather event during the Voyager 2 visit that led to powerful high-frequency waves, the most intense observed over the entirety of the Voyager 2 mission. In 1986, scientists thought that these waves would scatter electrons to be lost to Uranus’s atmosphere. But since then, Allen said, scientists have learned that those same waves under certain conditions can also accelerate electrons and feed additional energy into planetary systems.

“In 2019, Earth experienced one of these events, which caused an immense amount of radiation belt electron acceleration,” said SwRI’s Dr. Sarah Vines, a co-author of the paper. “If a similar mechanism interacted with the Uranian system, it would explain why Voyager 2 saw all this unexpected additional energy.”

But these findings also raise a lot of additional questions about the fundamental physics and sequence of events that would enable these intense wave emissions.

“This is just one more reason to send a mission targeting Uranus,” Allen said. “The findings have some important implications for similar systems, such as Neptune’s.”

Reference: “Solving the Mystery of the Electron Radiation Belt at Uranus: Leveraging Knowledge of Earth’s Radiation Belts in a Re-Examination of Voyager 2 Observations” by R. C. Allen, S. K. Vines and G. C. Ho, 21 November 2025, Geophysical Research Letters. DOI: 10.1029/2025GL119311

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