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| NASA’s Voyager 2 captured this image of Uranus during its 1986 flyby, and new research using mission data reveals that a solar wind event during the flyby may explain the long-standing mystery of the planet’s magnetosphere. |
NASA’s Voyager 2 flyby of Uranus in 1986 provided scientists with their first close-up look at the planet, but also raised new questions about its strange behavior. Among the mysteries was the planet's magnetosphere, which displayed unexplained patterns of energized particles, defying expectations of how magnetic fields should work. New research analyzing the data from that flyby has revealed the cause of these anomalies: an unusual space weather event that compressed Uranus' magnetic field just before the spacecraft's arrival.
This temporary compression, caused by solar wind, altered the magnetosphere in a way that occurs only about 4% of the time, offering a new explanation for the perplexing observations. "If Voyager 2 had arrived just a few days earlier, it would have observed a completely different magnetosphere," said Jamie Jasinski of NASA’s Jet Propulsion Laboratory, lead author of the study published in Nature Astronomy.
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| The first panel of this artist’s concept shows Uranus’s magnetosphere before Voyager 2’s flyby, while the second panel illustrates how unusual solar weather during the 1986 flyby gave scientists a skewed view of the magnetosphere. |
Magnetospheres play a critical role in protecting planets from the solar wind by acting as shields, much like Earth’s magnetic field does. This is why scientists were particularly interested in studying Uranus' magnetosphere, which, during the Voyager 2 flyby in 1986, presented some perplexing anomalies. The spacecraft observed intense electron radiation belts—second only to Jupiter’s—yet there appeared to be no clear source for the energized particles feeding these belts.
This was especially puzzling because Uranus’ five major moons, which orbit within the magnetosphere, should have been producing water ions, as seen with moons around other outer planets. Initially, scientists speculated that these moons were inactive, with no ongoing geological activity contributing to the plasma.
The mystery of Uranus' magnetosphere has now been partly solved. New analysis of Voyager 2's 1986 data reveals that a solar wind event prior to the spacecraft's flyby compressed the planet’s magnetosphere, temporarily driving out plasma. This solar wind also briefly intensified the magnetosphere's dynamics, injecting electrons into the radiation belts, which explained their unusual intensity. The findings suggest that the planet's five major moons may not be inactive after all; they could have been contributing ions to the magnetosphere throughout, despite the earlier absence of observable plasma.
These revelations have sparked renewed interest in Uranus, a target for future exploration as identified in the 2023 National Academies' Decadal Survey. Linda Spilker, a key scientist from the Voyager 2 mission, recalled the excitement of the flyby and the mysteries it uncovered. "The flyby was packed with surprises, and we were searching for an explanation of its unusual behavior," said Spilker, who is now leading the science team for the Voyager mission. This new work explains some of the apparent contradictions and will change our view of Uranus once again.Voyager 2, now over 13 billion miles from Earth, continues to offer valuable insights as it travels through interstellar space.
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