New analysis of data from NASA's Voyager 2 spacecraft revealed that mysteries about Uranus's magnetosphere, which have puzzled scientists for decades, may have been explained by unexpected data collected during an unusually powerful solar storm. Researchers reanalyzed eight months of data around the time of Voyager 2's visit to Uranus and found that the source of the mystery is a cosmic coincidence related to an intense solar wind event that occurred just before the flyby.
"We found that the solar wind conditions present during the flyby only occur 4 percent of the time. The flyby occurred during the maximum peak solar wind intensity in that entire eight-month period," said Jamie Jasinski, a space plasma physicist at NASA's Jet Propulsion Laboratory and lead author of the study.
"If Voyager 2 had arrived a week earlier, it would have observed a completely different magnetospheric environment," he added.
During its 1986 flyby, Voyager 2 observed that Uranus's magnetosphere was devoid of plasma, which is prevalent around other planets, and found unexpectedly intense electron radiation belts. These observations led scientists to believe that Uranus's magnetosphere was unique and lacking in plasma sources. However, the new findings suggest that the intense solar wind event compressed Uranus's magnetosphere to about 20 percent of its usual volume, which might have skewed the data collected by Voyager 2.
The compression shrank Uranus's magnetosphere from an estimated 28 times Uranus's diameter to about 17 times it within a week. This intense solar wind event created conditions around the planet that are usually only seen about 4 percent of the time. "We observed this empty magnetosphere," Jasinski noted, which contributed to the extreme magnetospheric environment observed around Uranus. He emphasized that "a future mission to Uranus is crucial to understanding not only the planet and magnetosphere, but also its atmosphere, rings, and moons."
Dr. William Dunn, co-author of the study from UCL's Department of Physics and Astronomy, explained, "This new study shows that a lot of the planet's bizarre behaviour can be explained by the scale of the space weather event that occurred during that visit." He added, "We now know even less than we thought about what a typical day in the Uranian system might look like and are even more in need of a second spacecraft to visit to truly understand this mysterious, icy world."
The researchers wrote, "If the spacecraft had arrived only a few days earlier, the upstream solar wind dynamic pressure would have been about 20 times lower, resulting in a dramatically different magnetospheric configuration." They concluded that future missions to Uranus are required to truly understand the planet's magnetosphere, as the observations made by Voyager 2 should not be assigned any typicality regarding Uranus's magnetosphere.
The new analysis also has implications for Uranus's moons. The missing plasma was particularly puzzling because scientists knew that the five major Uranian moons should have produced water ions, yet they concluded that the moons must be inert with no ongoing activity. Jasinski said, "The solar wind could have essentially eradicated all the evidence of active moons just before the flyby happened." This suggests that Uranus's largest moons, Titania and Oberon, might even have global oceans, making it easier for future missions to search for oceans beneath their surfaces.
Linda Spilker of NASA's Jet Propulsion Laboratory, who was among the Voyager 2 mission scientists during the Uranus flyby in 1986, said, "The flyby was packed with surprises, and we were searching for an explanation of its unusual behavior. The magnetosphere Voyager 2 measured was only a snapshot in time." She added, "This new work explains some of the apparent contradictions, and it will change our view of Uranus once again."
Voyager 2 is now 47 years and two months into its mission, traveling through interstellar space at 34,391 miles per hour (55,347 kilometers per hour), and is expected to keep operating into the late 2020s. The spacecraft is so distant that it takes light over 19 hours to travel from it to Earth.
Sources: Gizmodo, NASA, New Scientist, The New York Times, Newsweek, Cosmos, The Independent, Yahoo News, The Straits Times, Science Alert, Nature, Mirage News, Science News
This article was written in collaboration with generative AI company Alchemiq