Scientists have long puzzled over the strange magnetic environments surrounding Uranus and Neptune. When NASA’s Voyager 2 spacecraft flew past these distant worlds in the 1980s, it revealed magnetic fields that were heavily tilted and offset from the planets’ centers. Unlike Earth, which has a relatively orderly field aligned with its rotation axis, these ice giants possess distorted magnetic structures that have defied simple explanation for decades.
A new study published in Communications Physics offers a potential solution. Researchers from The University of Texas at Austin, along with collaborators from the University of California, Los Angeles, Imperial College London, and Northumbria University, suggest that the answer lies in how materials conduct electricity under extreme pressure. Their computer models indicate that electrical conductivity increases with depth inside these planets, fundamentally altering how their magnetic dynamos operate.
Conductivity Changes Drive Magnetic Chaos
Planetary magnetic fields are generated by dynamos, processes where moving fluids capable of conducting electricity create magnetic forces. On Earth, this occurs in the outer core, a layer of molten metal surrounded by solid rock. The circulation of liquid iron, combined with the planet’s rotation, produces a magnetic field that resembles a giant bar magnet. Earth’s main magnetic axis is tilted by only 11 degrees relative to its rotation axis.
Uranus and Neptune tell a different story. Uranus has a magnetic dipole tilted by 59 degrees, while Neptune’s is tilted by 47 degrees. These extreme angles suggest that the internal structures of these planets differ significantly from terrestrial worlds. Both are classified as ice giants, a term that reflects their composition of hydrogen, helium, water, ammonia, methane, and rocky material rather than their temperature.
Chi Yan, the study’s lead author and a research associate at the UT Jackson School of Geosciences, noted that the combination of the planets’ enormous size and unusual chemical makeup likely drives their unique magnetism. “Deep inside Uranus and Neptune, pressures and temperatures become extremely high,” Yan said. “Under these conditions, which can cause water molecules to break apart into ions, the material may become increasingly electrically conductive with depth.”
Ions are electrically charged particles that carry electric current. If the interior materials become more conductive at greater depths, the resulting dynamo would generate a magnetic field that is less stable and more complex than those found on Earth. The researchers developed simulations to test this hypothesis, assuming that electrical conductivity increases deeper inside the planets. They examined how circulating fluids, temperature changes, and magnetic forces interact over time.
Rapid Shifts in Magnetic Axes
The simulations produced a surprising result: the magnetic fields of Uranus and Neptune may be far less stable than previously thought. The models suggest that their magnetic axes could undergo substantial changes in relatively short periods. In some scenarios, the magnetic tilt shifted by tens of degrees within only a few decades.
This volatility stands in sharp contrast to Earth’s magnetic behavior. “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. In others it shifts only slightly over the same span.”
These dramatic changes remain predictions from computer models rather than confirmed observations. However, scientists have a method to look for evidence of these shifts. Researchers are currently examining detailed infrared images of Uranus and Neptune captured by the James Webb Space Telescope (JWST). They are focusing on the planets’ auroras, which form when charged particles from the Sun interact with gases in their atmospheres.
Auroras are closely connected to planetary magnetic fields, making them valuable clues to what is happening far above the planets’ hidden interiors. Changes in the appearance and arrangement of these glowing atmospheric features could help researchers determine whether the magnetic poles have shifted since Voyager 2’s encounters. The ionosphere, a region of the upper atmosphere containing electrically charged particles, also provides data on magnetic activity.
“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, promises 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.
The research team hopes to combine Webb’s auroral observations with Voyager 2’s original magnetic field measurements and the new dynamo simulations. Together, these sources of evidence could provide the clearest picture yet of how the magnetic fields of Uranus and Neptune are arranged today. While improved simulations and powerful telescopes offer new insights, scientists emphasize that fully understanding the planets’ deep interiors will require new spacecraft missions to these distant worlds.
Source: ScienceDaily
