Uranus has a weird magnetic field that's stumped scientists for 40 years

Computer modeling by researchers from the United States and the United Kingdom, based on Voyager 2 data, may explain the unusual magnetic fields of Uranus and Neptune, according to UA.NEWS. The only spacecraft to visit both ice giants, Voyager 2 flew past Uranus in January 1986 and Neptune in August 1989. It found that Uranus's magnetic field is tilted 59 degrees from the planet's rotational axis and is not centered in the core, while Neptune's field is tilted by 47 degrees and also offset from the center. By comparison, Earth's magnetic field is tilted only 11 degrees relative to its rotational axis.

Previously, one possible cause of Uranus's tilt was considered to be an ancient collision with an Earth-sized planet that may have tipped the ice giant over. However, the similar structure of Neptune's field indicates that the explanation should be sought in the internal properties of both planets. The authors modeled the dynamo effect — a process in which convective motion of an electrically conductive liquid in a rotating body creates and sustains a magnetic field. On Earth, this liquid is molten iron in the outer part of the core.

Uranus and Neptune are significantly more massive than Earth: their masses are 14.5 and 17 Earth masses, respectively. Under high pressure and temperature in their interiors, water molecules can break down into ions, making matter more electrically conductive with depth. Models that accounted for this factor and the planets' composition reproduced the anomalous structure of their magnetic fields.

The simulations also indicate that the magnetic fields of the ice giants can change significantly over several decades. During some periods, the magnetic field's tilt may fluctuate by tens of degrees, whereas Earth's magnetic tilt changes by about one degree over 50 years. Scientists hope to compare the models and Voyager 2 data with observations of infrared auroras on Uranus and Neptune, which co-author Tom Stallard is conducting using the James Webb Space Telescope. NASA has identified a new mission to Uranus in the early 2040s as one of its priorities. The study's results were published on November 3 in the journal Communications Physics.