Voyager 2 Measured a Rare Anomaly When It Flew Past Uranus, Skewing Our Knowledge of the Planet for 40 Years, Study Suggests

In 1986, when NASA’s Voyager 2 flew by the mysterious Uranus, it gave scientists their first close-up peek into the solar system’s seventh planet. The discoveries from that singular visit still provide much of astronomers’ modern understanding of the strange, “ice giant” world. But now, a new study reveals Uranus was experiencing a rare solar wind event at the time of the flyby, suggesting the understanding that came from the Voyager 2 visit may have been skewed.

In a paper published on Monday in Nature Astronomy, researchers argue that if the spacecraft had arrived at Uranus just a few days earlier, it would have discovered something else.

“The spacecraft saw Uranus in conditions that only occur about 4 percent of the time,” says Jamie Jasinski, a physicist at NASA’s Jet Propulsion Laboratory and lead author of the study, in a statement from NASA.

Those unusual conditions have to do with Uranus’ magnetosphere—a planet’s protective magnetic bubble that shields it from the solar wind. That 1986 visit encountered an empty magnetosphere around Uranus, oddly devoid of plasma. Astronomers concluded the planet was different compared to others in the solar system, but the new findings suggest its magnetosphere was just being squashed by a solar wind event that sent a stream of plasma and charged particles toward the planet.

After traveling some 1.8 billion miles to reach Uranus 38 years ago, Voyager 2 gathered its data on the planet in less than six hours, discovering ten new moons and two rings alongside the void magnetosphere.

When Jasinski and his colleagues presented the new research this past summer, it was a surprise for Fran Bagenal, an astrophysicist at the University of Colorado, Boulder, who worked with the Voyager plasma science team, reports the New York Times’ Jonathan O’Callaghan.

“Why didn’t we see this?” Bagenal tells the outlet. “I was kicking myself. It was completely out of the blue.”

Jasinski had always wondered about the results of the flyby, because it provided only a small peek into the planet, he told the Washington Post’s Rachel Pannett in an email. Jasinski has experience with missions that orbited planets and observed changes over much longer periods of time, which led him to believe the conclusions about Uranus may have been flawed.

“The extreme type of measurements Voyager 2 took always made me wonder if we just caught Uranus at a very specific moment in time,” he tells the Washington Post.

For scientists, learning more about magnetospheres helps reveal how different planets function. Using the knowledge from the 1986 flyby, astronomers had concluded that the missing plasma around Uranus also meant its moons were inactive.

But the new research shows that might not be the case. If the missing plasma was indeed due to solar wind—which would have compressed the planet’s magnetic bubble and driven plasma out—it allows for the possibility that Uranus’ five major moons might indeed be geologically active.

The solar wind event might also have affected the planet’s radiation belts, regions with lots of energetic and charged particles, by infusing them with even more electrons. This would explain why Voyager 2’s observations showed Uranus’ radiation belts as some of the most intense in our solar system, second only to Jupiter.

Linda Spilker, a planetary scientist at NASA who was not involved in the new study, remembers being glued to the images from the 1986 flyby with anticipation and excitement. “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 says in the statement.

NASA might soon expand its knowledge about Uranus in a mission to the planet, marked as a priority by scientists as part of the most recent Planetary Science and Astrobiology Decadal Survey. They recommended that NASA put a spacecraft into orbit around the mysterious planet and release a probe into its atmosphere to better understand the solar system’s origin and evolution.

“The Uranus system is one of the big blank spots that are left on our map,” Francis Nimmo, a planetary scientist at the University of California, Santa Cruz, told Scientific American’s Shannon Hall last year.

For now, “this new work explains some of the apparent contradictions,” from the Voyager 2 flyby, Spilker adds in the NASA statement, “and it will change our view of Uranus once again.”

Alexa Robles-Gil | | READ MORE

Alexa Robles-Gil is a bilingual science journalist based in New York City. Her work has appeared in the Guardian, Undark, Inside Climate News and more.