Voyager 2 erred about radiation environment on Uranus. Blame wrong timing

NASA's Voyager 2 probe flew by Uranus in 1986, providing the first observation of the ice giant that lives in the farthest reaches of the solar system. This event proved historic as scientists learned about what the planet was like, its moons and also raised certain mysteries. One of them was the presence of an electron belt of a much higher energy level than expected. Since then, scientists have been puzzled about how the Uranian system supports such an enormous amount of trapped electron radiation. They also studied other gas giants outside the solar system and compared the phenomenon observed on Uranus. Turns out, it was all for nothing. A study has found that Voyager 2 simply scanned the planet at a time when another cosmic occurrence was also going on, causing the mysterious observation.

Scientists at the Southwest Research Institute (SwRI) have pointed out that what Voyager 2 saw was happening because of a solar wind structure. They suggest that a "co-rotating interaction region" was passing through the system right when Voyager 2 made the flyby. Space physicist and the Lead Scientist of the SwRI's Space Sciences Division, Dr Robert C. Allen, led the study and was assisted by SwRI Lead Scientist Sarah Vines. They published their findings in Geophysical Research Letters.

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Voyager 2 encountered Uranus at the wrong time

Voyager 2 measured the radiation environment at Uranus, which formed the basis for the scientific belief that it has a weaker ion radiation belt and a very intense electron radiation belt. But when Allen's team analysed the data again, they found that this observation was not made during normal solar wind conditions and that at the time, a transient solar wind event was passing through the system. According to them, Voyager 2 recorded the most powerful high-frequency waves at this point during its entire mission.

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"Science has come a long way since the Voyager 2 flyby. We decided to take a comparative approach, looking at the Voyager 2 data and comparing it to Earth observations we've made in the decades since," said Dr Allen in a statement. Something similar happened with Earth in 2019, when solar winds caused an "immense amount of radiation belt electron acceleration." This explains why "Voyager 2 saw all this unexpected additional energy," he said.