Wacky magnetic fields of ice giants may stem from conductivity changes in their deep interiors

Wacky magnetic fields of ice giants may stem from conductivity changes in their deep interiors Sadie Harley Scientific Editor Robert Egan Senior Editor When NASA's Voyager 2 robotic probe flew by Uranus and Neptune in the 1980s, it uncovered an anomaly: their magnetic fields are highly disordered, unlike Earth's, which has well-defined north and south poles. New research suggests that changes in electrical conductivity deep inside Uranus and Neptune may be key to explaining their unusual magnetic fields and how they could evolve over time. The finding comes from a study published in Communications Physics, led by researchers at The University of Texas at Austin, with collaborators from the University of California, Los Angeles, Imperial College London and Northumbria University. Different interiors, different magnetic fields Magnetic fields are created as electrically conducting fluids move deep inside a planet—this natural process is called a dynamo. On Earth, the planet's outer core is composed of liquid metal surrounded by a mostly solid layer of rock. Convection of molten iron, influenced by Earth's rotation, generates a magnetic field that resembles a bar magnet with strong north and south poles. That's what makes a compass align north-south. Earth's magnetic arrangement, or its dipole, is nearly upright, tilted relative to its rotational axis by only 11 degrees. In contrast, Uranus' magnetic dipole is tilted by 59 degrees and Neptune's by 47 degrees. While the precise materials making up Uranus and Neptune remain unknown, these planets—about four times wider than Earth—have been dubbed ice giants. They are thought to consist mainly of hydrogen, helium, water, ammonia, methane and rocky material. According to the study's lead author, Chi Yan, a research associate at the UT Jackson School of Geosciences, the planets' large size combined with their geochemical composition could be a recipe for the tilted magnetic fields. "Deep inside Uranus and Neptune, pressures and temperatures become extremely high," said Yan. "Under these conditions, which can cause water molecules to break apart into ions, the material may become increasingly electrically conductive with depth." Simulations point to rapidly shifting fields The researchers used computer simulations to reproduce the unusual magnetic fields observed by Voyager 2. Assuming electrical conductivity increases at greater depths, and considering diverse interior configurations, they simulated how fluid motion, temperature and magnetic fields evolve together to generate the planets' dynamos. Their models suggest that Uranus' and Neptune's magnetic fields could change substantially within decades and may be configured differently than they were during the Voyager 2 mission. "Earth's magnetic tilt drifts by only a degree or so over 50 years," said Yan. "Our models show the ice giants can behave very differently. In some stretches the tilt swings by tens of degrees within decades. In others it shifts only slightly over the same span." Auroras could reveal today's magnetic fields In the meantime, researchers are analyzing high-resolution images from the James Webb Space Telescope (JWST), which is sensitive to infrared light. The telescope observes Uranus' and Neptune's auroral emissions, which occur when charged particles from the sun interact with gases in the planets' atmospheres. These emissions can hold clues about whether the dipole has shifted. "We are busy working on what's contained within these observations, but the shape and structure of the aurora, as well as other weird patterns in the ionosphere, promise to provide us with a way of understanding how the magnetic fields have changed, an important stepping stone," said Tom Stallard, a professor at Northumbria University who led the JWST observation campaign and reviewed the paper for the journal. The researchers plan to combine data from the JWST auroral images, Voyager 2 magnetic field observations and dynamo simulations to estimate how the planets' magnetic fields might be configured today. However, to properly understand the planets' interiors, the researchers say additional missions back to the ice giants are necessary. Publication details Chi Yan et al., Electrical conductivity structure drives anomalous and potentially time-varying magnetic fields at Uranus and Neptune, Communications Physics (2026). DOI: 10.1038/s42005-026-02841-y Journal information: Communications Physics Provided by University of Texas at Austin