Because ice giant planet Uranus rotates on its side, its magnetosphere tumbles asymmetrically in relation to the solar wind, causing it to open and close every day.
A planet’s magnetosphere is the region defined by its magnetic field and anything trapped within that field.
Earth’s magnetosphere opens and closes only in response to changes in the solar wind, the flow of charged particles from the Sun. Because our planet’s magnetic field is aligned with its rotation axis, its magnetosphere, which always faces the Sun, spins together with its rotation.
In contrast, Uranus’ magnetic field is lopsided and has a 60-degree tilt to its axis of rotation. As a result, the planet’s magnetic field tumbles asymmetrically in relation to the solar wind.
“Uranus is 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’s magnetosphere goes from open to closed on a daily basis,” said said Carol Paty of the Georgia Institute of Technology and co-author of a study on the findings published in the Journal of Geophysical Research: Space Physics.
The research team used data from NASA’s Voyager 2, which flew by Uranus in 1986, along with numerical computer models that simulated its global magnetosphere.
In Uranus’ case, its magnetic field often opens in one direction, which lets the solar wind flow into the magnetosphere, then subsequently closes, deflecting the solar wind away from the planet.
Throughout the solar system, magnetic fields reconnect when the direction of the interplanetary magnetic field, which originates from the Sun, lies opposite the alignment direction of a planet’s magnetic field.
When magnetic fields reconnect, the planetary system involved experiences a boost in solar energy, often producing auroras.
NASA’s Hubble Space Telescope can barely see auroras on Uranus because the planet is so distant, and the telescope is not capable of measuring its magnetic field.
Understanding ice giants is important because many exoplanets, based on their sizes, appear to be ice giants. Through increased study of the processes by which magnetospheres and misaligned magnetic fields protect a planet from stellar radiation, scientists improve their understanding of the habitability of individual worlds, said study leader Xin Cao, also of Georgia Tech.