Unusual Incident Occurred during Voyager 2's Approach to Uranus in 1986
A recent examination of 38-year-old Voyager 2 data reveals that the daring spacecraft passed Uranus at an unusual moment when the planet's magnetosphere was distorted by solar particles.
The study, published today in Nature Astronomy, suggests that Uranus' magnetic structure may not be as we initially perceived. Initial analysis of the Voyager 2 data indicated that Uranus' magnetosphere, the region influenced by its magnetic field, was devoid of plasma, a common component in other planetary magnetospheres.
The data also showed that Uranus had unusual belts of energetic electrons, unlike other planets. Jokes aside, Uranus' environment was strikingly dissimilar to the rest of our solar system.
Scientists propose that these unusual conditions were due to a powerful solar wind blast that warped the magnetosphere just as Voyager 2 approached in 1986.
Jamie Jasinski, a planetary scientist at NASA's Jet Propulsion Laboratory and Caltech, and the study's lead author, stated in an email to Gizmodo, "These were two major mysteries left over from the Voyager 2 flyby, both of which can be reasonably explained by the arrival of an intense solar wind event that compressed the magnetosphere dramatically just before the flyby began."
"If we had arrived a week earlier with Voyager 2, the spacecraft would have recorded different measurements, and our discoveries would have been significantly different," Jasinski added. "Voyager 2 arrived at exactly the wrong moment!"
According to the research team, the rare compression of the magnetosphere occurs only 4% of the time around Uranus. The remaining 96% of the time, Uranus' magnetosphere is not as extreme. The findings also suggest that during the Sun's 11-year cycle's lowest point, Uranus experiences alternating periods of disturbed solar wind that affect its magnetosphere. The magnetosphere's "open" or "closed" state may be influenced by Uranus' extreme tilt, which is unusual in comparison to the solar system's orbital plane.
Based on the Voyager 2 data, the team concluded that "the Uranian magnetosphere may have had two cycles at the time of the Voyager 2 flyby: the first varying on a diurnal timescale due to the 'switch-like' or 'open-closed' processes mentioned above, and the second due to the varying solar wind conditions."
Voyager 2 is the only spacecraft to have visited Uranus and Neptune and discovered 16 moons and six planetary rings as it left our solar system. Voyager 2 is now 47 years and two months into its mission, traveling at 34,391 miles per hour (55,347 kilometers per hour) through interstellar space. The mission is approximately 13 billion miles (20.9 billion kilometers) from Earth, over 138 times the distance between Earth and the Sun. It takes light over 19 hours to reach Earth from the spacecraft.
Since 1986, NASA has implemented power-saving measures that have left only four of the Voyager spacecraft instruments operational: the two missions' cosmic ray subsystems, magnetometers, and instruments for measuring charged particles and electrical fields.
Carol Paty, a planetologist at the University of Oregon who is not affiliated with the recent study, said, "It's always wonderful when you can go back to data that's decades old with fresh eyes and fresh perspective."
The study suggests that Voyager 2 observed a particularly extreme event involving Uranus' magnetosphere, but Paty notes that it would be an overstatement to assume that Uranus' typical state is similar to other planets in our solar system. Uranus' magnetosphere remains highly asymmetric, and its extreme tilt results in some of the most extreme seasons in our solar system.
"What we know from looking at this paper, just from the upstream solar wind data analysis alone, the solar wind is quite variable even at Uranus' orbital distance," Paty added. "And that variability means that this system is going to be incredibly dynamic and responsive to the solar wind."
Uranus is an intriguing subject for astrobiology—life beyond Earth. In 2022, a 780-page report by the National Academies of Sciences, Engineering, and Medicine called for a Uranus orbiter capable of mapping the planet's gravitational and magnetic fields and launching an atmospheric probe.
Separately, planetary scientists have advocated for a Uranus mission; Uranus has many mysteries and no spacecraft has visited it since Voyager 2. The mission's images of the planet and its moons remain the primary data source for planetary scientists producing new research about Uranus, as indicated by a recent study on the possibility of a subsurface ocean on Miranda, one of Uranus' moons.
"Titania and Oberon are the prime suspects for housing oceans due to their larger size compared to other moons, allowing them to hold onto heat more effectively and thus remain warmer. Consequently, they're less likely to be entirely frozen. According to Jasinski, given the team's examination of Voyager's data, the potential liquid components within these moons could be identified with more ease than anticipated."
"It's about time we swung by Uranus, but until then, researchers are determined to squeeze out every drop of knowledge from the data gathered by Voyager, which is now over three decades old."
The discovery of Uranus' unusual magnetic structure and plasma-devoid magnetosphere can be attributed to advances in technology and scientific analysis, enabling us to re-examine old Voyager 2 data with new insights. Moreover, understanding Uranus' magnetosphere could pave the way for future space missions, particularly in the field of astrobiology, as it could provide clues about the existence of subsurface oceans on its moons.
