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Uranus has the weirdest magnetic field in our solar system, and it just got weirder. A new model suggests that the edge of its magnetic field bubble could be slamming open and shut every day.

Most of the planets in our solar system rotate around roughly similar axes, spinning in the same plane as their orbit. Their magnetic fields are aligned with these axes, with field lines emerging from the centres of the planets near their north and south poles and wrapping them in magnetospheres 鈥� protective bubbles of magnetism.

Uranus is not like most of the planets. It rotates on its side, tilted almost 98 degrees from the plane of its orbit around the sun. The axis of its magnetic field is tilted too, at a 59-degree angle from the rotational axis. The magnetic field is also off-centre, with the field lines emerging about a third of the way toward the south pole.

All of this makes Uranus鈥檚 magnetosphere a total mess. 鈥淎s it is tumbling around, the magnetosphere鈥檚 orientation is changing in all sorts of directions,鈥� says at the Georgia Institute of Technology in Atlanta.

To study the effects of this tumbling, Paty and her student created a model of the magnetosphere and its interactions with the solar wind, a stream of charged particles blown out by the sun.

Magnetic shield

The magnetosphere acts as a barrier to the solar wind: when the two are moving in the same direction, the solar wind slides off it like water off a duck鈥檚 back. But just as when water hits a duck鈥檚 feathers from the tail end, the duck gets wet, so when the solar wind blows toward Uranus at the right angle, the planet鈥檚 magnetic field lines up with the solar wind鈥檚 and lets some particles flow through.

This process, called magnetic reconnection, occurs occasionally near Earth鈥檚 poles, where the influx of particles from the solar wind can lead to intensified auroras. On Uranus, Paty and Cao found that it should happen every single day (roughly 17 Earth hours), switching the magnetosphere鈥檚 protection on and off. This could lead to an aurora there as well.

But it鈥檚 hard to know what exactly is going on at Uranus, since the only close-up observations we have are from 1986, when the Voyager 2 spacecraft whizzed past over the course of five days.

鈥淲e caught a glimpse of a mystery when we flew by,鈥� says Paty. 鈥淲e went inside Uranus鈥檚 magnetic field and suddenly it didn鈥檛 look like Earth or Jupiter or Saturn at all.鈥� That brief snapshot isn鈥檛 much, but Paty鈥檚 model matches it perfectly.

鈥淚t鈥檚 great that it matches as well as it does with the one fly-by that we have of Uranus,鈥� says at the University of Iowa. 鈥淏ut the real test would be sending an orbiter there and getting lots of data in different conditions and seeing if the model still matches.鈥� NASA has plans in the works to send a new probe to Uranus in 2034, but no mission has been approved yet.

Ice giants

Paty hopes that as our tally of exoplanets grows, a greater understanding of Uranus will help us make inferences about those distant worlds, many of which are ice giants like Uranus and Neptune. Figuring out how their magnetic fields protect them (or not) from the stellar wind could be key to determining what their surfaces are like.

It may even lead to insights closer to home, by teaching us more about Earth鈥檚 relatively simple magnetic field.

鈥淟ooking at how Uranus鈥檚 complicated, strange magnetosphere works helps us understand how all the other systems work,鈥� says Hospodarsky. 鈥淚t鈥檚 sort of like doing an experiment one way and then turning it upside down and starting again. If it still works, your theories are good.鈥�