No way to sugarcoat this: I'm afraid Uranus opens and closes to accept particle streams

Scientists digging through old readings from NASA’s Voyager 2 mission in 1986 have found that Uranus’ magnetic field swings open and shut like the aperture of a revolving door.

Uranus doesn’t just have a funny name, it has a silly orbit too. It’s the only planet in the Solar System to lie on its side – almost 98˚ from its plane of orbit around the Sun. The direction of rotation and its magnetic field lines are lopsided; its magnetic field is tilted 60˚ from its axis.

The incoming stream of energetic particles making up the solar wind flow strike Uranus’ magnetic field asymmetrically as the ice giant completes a full spin every in 17 hours and 14 minutes.

Carol Paty, associate professor at Georgia Tech and co-author of the study published this month in the Journal of Geophysical Research: Space Physics, called the planet a “geometric nightmare”.

“The magnetic field tumbles very fast, like a child cartwheeling down a hill head over heels. When the magnetized solar wind meets this tumbling field in the right way, it can reconnect and Uranus’ magnetosphere goes from open to closed to open on a daily basis.”

Numerical simulations of the planet’s magnetosphere show that it closes off and blocks out the harmful stream of radiation if its magnetic field is aligned with the direction of the solar wind. But if it’s blowing in at a right angle to the planet’s magnetic field, then it can cut through Uranus’ magnetosphere, letting in a surge of solar energy.

A similar process, called magnetic reconnection, is common in the solar system. It happens near Earth’s poles, and leads to a rush of particles streaming into the atmosphere creating the phenomenon known as the Aurora Borealis.

The researchers believe auroras are possible at a range of latitudes on Uranus, but the dancing light patterns are hard to observe since Uranus is nearly 2 billion miles away. The Hubble Space Telescope can sometimes catch glimpses of auroras flashing on the distant planet, but it cannot study them directly.

Xin Cao, lead author of the study and PhD student at Georgia Tech, said wonky magnetic fields might actually be the norm for planets.

"The majority of exoplanets that have been discovered appear to also be ice giants in size. Perhaps what we see on Uranus and Neptune is the norm for planets: very unique magnetospheres and less-aligned magnetic fields. Understanding how these complex magnetospheres shield exoplanets from stellar radiation is of key importance for studying the habitability of these newly discovered worlds." ®