“Deep inside Uranus and Neptune, pressures and temperatures become extremely high,” said Chi Yan, a research associate at the UT Jackson School of Geosciences.
Scientists may finally understand why the ice giants of the outer solar system possess distorted, highly tilted magnetic fields, according to a study published on November 3 in Communications Physics.
Only one spacecraft has ever visited the distant ice giants. The Voyager spacecraft spent past Uranus in January 1986 and Neptune in August 1989. During those flybys, instruments discovered that both distant planets possess strangely distorted and dramatically tilted magnetic fields.
While Earth’s magnetic axis is tilted by just 11 degrees from its rotation axis, Uranus’ magnetic dipole is tilted by 59 degrees and Neptune’s by 47 degrees. Uranus’ magnetic field was also offset from its rotational axis by 59 degrees. It isn’t even centered on the planet’s core, sitting only two-thirds of the way down.
Planetary magnetic fields arise from the dynamo effect. This is driven by the convective motion of electrically conducting fluids inside a rotating body. Uranus and Neptune are classified as ice giants. Their interiors contain hydrogen, helium, water, ammonia, methane, and rocky material surrounding a probable core.
The study’s lead author, UT Jackson School of Geosciences research associate Chi Yan, suggests that these planets’ massive scale and distinctive chemical composition could explain why their magnetic fields are so peculiar.
“Under those conditions, which can cause water molecules to break apart into ions, the material may become increasingly electrically conductive with depth,” Yan told Space.
Researchers built computer simulations incorporating this depth-dependent electrical conductivity. They modeled fluid motion, temperature changes, and magnetic forces. The resulting models successfully reproduced the bizarre field structures recorded by Voyager 2. They also revealed that the planets’ internal dynamos may be surprisingly dynamic.
“Earth’s magnetic tilt drifts by only a degree or so over 50 years,” Yan said.
“Our models show the ice giants can behave very differently. In some stretches, the tilt swings by tens of degrees within decades,” Yan added in findings published by Space.
These model predictions suggest that the magnetic fields of Uranus and Neptune today may differ significantly from the measurements collected during the 1980s flybys. To test these computer simulations without waiting for a new spacecraft, researchers are turning to modern telescopes.
Auroras form when solar wind particles interact with a planet’s magnetic field and upper gases. This provides clues about magnetic configurations.
Financial backing for the study was provided by the Science and Technology Facilities Council, the National Aeronautics and Space Administration (NASA), and The University of Texas Institute for Geophysics (UTIG), which is part of the Jackson School of Geosciences. Additional scientific contributions came from the University of California, Los Angeles, and Imperial College London.
While space agencies plan future exploration—including NASA prioritizing a new mission to return to Uranus in the early 2040s and the China National Space Administration planning the Tianwen-4 mission to Jupiter in 2029 with a small probe continuing onward to Uranus—current researchers are combining JWST data, Voyager 2 records, and new dynamo models to map the ice giants as they exist today.
