A chance encounter 40 years ago led us to believe that Uranus could not harbor life

When NASA’s Voyager 2 flew over Uranus in 1986, the information it collected shocked scientists. Unlike every other planet in the solar systemUranus seemed barren, as did its moons. Now, nearly forty years later, astronomers are reconsidering why Uranus seemed so inactive on that fateful day. They have discovered that Voyager 2’s flyby was a freak event: the spacecraft passed over Uranus during an ‘extreme’ solar storm, effectively ruining any chance Voyager 2 had of getting an accurate snapshot of the planet’s magnetic field .

Magnetospheres, or the magnetic fields that surround celestial bodies, are an essential part of any planet that harbors life. By trapping gases in a planet’s atmosphere and shielding its surface from harmful solar radiation, these invisible guardians protect the planet from the harsh erosion that would otherwise deplete the oceans and kill all potential life. When Mars lost its magnetospherethe whole planet changed; If the Earth’s magnetic field were to disappear tomorrow, we would gradually disappear too.

When Voyager 2 passed 50,000 feet above Uranus decades ago, it clocked a deeply distorted magnetosphere, leading researchers to believe that Uranus was barren: the planet could harbor no water, no useful gases and no life. Because Uranus’ magnetosphere also surrounded the five largest moons, scientists’ assumption about inactivity extended to them as well. Uranus wasn’t just frigid and bizarrely tilted; it was even devoid of the heap for life.

But researchers at NASA’s Jet Propulsion Laboratory (JPL) recently revisited Voyager 2 data and were rewarded for their efforts. In a new paper for Nature Astronomythey reveal that Uranus’ “inexplicably intense” radiation and depleted magnetosphere are not the planet’s typical state. Instead, these conditions are thought to exist around Uranus only 5% of the time; they coincidentally manifested during Voyager 2’s flyby, which coincided with an aggressive solar storm.

Illustration of Uranus’ magnetic field. Credit: NASA

The team believes this storm was accompanied by a series of long plasma streams erupting from the sun’s surface as it rotated. This phenomenon is known as a ‘co-rotating interaction region’ or CIL and has also affected other planets in the past, including Earth, where it was activated geomagnetic storms– but was not considered a potential factor in the 1980s. Now JPL believes that a CIL has multiplied the pressure of the solar wind on Uranus’ magnetosphere by 20 times, effectively compressing the magnetic field to one-fifth of its typical volume.

“If the spacecraft had arrived just a few days earlier, the dynamic pressure of the upstream solar wind would have been ~20 times lower, resulting in a dramatically different magnetospheric configuration,” the team writes. ‘The interpretation of Uranus’ magnetosphere as extreme could simply be the product of a flight that took place under extreme upstream solar wind conditions.’

Despite excited speculation in some quarters online, JPL’s findings cannot confirm whether this is the case Uranus is capable of harboring life. Instead, the discovery brings us back to the potential for life or life-sustaining phenomena on Uranus – or its five largest moons. It will also guide NASA and other space agencies in building exploration equipment suitable for Uranus’ magnetosphere.