Researchers suggest that extreme pressures deep inside Uranus and Neptune cause water molecules to break apart into ions, increasing electrical conductivity with depth and creating strangely tilted magnetic fields. The findings, published in Communications Physics, could explain why these ice giant planets behave so differently from Earth.
Why Are Uranus and Neptune’s Magnetic Fields So Tilted?
When NASA’s Voyager 2 spacecraft flew past Uranus and Neptune in the 1980s, it discovered that both planets possess strangely distorted and dramatically tilted magnetic fields. Earth’s magnetic dipole is tilted by only 11 degrees from its rotation axis. In contrast, Uranus has a magnetic dipole tilted by 59 degrees, while Neptune’s is tilted by 47 degrees.
Planetary magnetic fields originate deep beneath the surface through a process called a dynamo, where moving fluids capable of conducting electricity generate magnetic forces. Uranus and Neptune are classified as ice giants. Scientists believe their cores contain rocky material alongside significant quantities of water, ammonia, methane, helium, and hydrogen, and each planet spans roughly four times the width of Earth.
How Extreme Pressures Change Electrical Conductivity
Chi Yan led a new study investigating these unusual planetary interiors at The University of Texas at Austin. Researchers from the University of California, Los Angeles, Imperial College London, and Northumbria University collaborated on the project.
“Deep inside Uranus and Neptune, pressures and temperatures become extremely high,” said Chi Yan, research associate at the UT Jackson School of Geosciences.
“Under these conditions, which can cause water molecules to break apart into ions, the material may become increasingly electrically conductive with depth,” said Yan.
Can Magnetic Poles Shift Within Decades?
The research team developed computer simulations to reproduce the magnetic fields recorded by Voyager 2. Their models assumed that electrical conductivity increases deeper inside the planets, examining how circulating fluids, temperature changes, and magnetic forces interact over time.
The simulations revealed that the magnetic fields of Uranus and Neptune may be far less stable than Earth’s. Their magnetic axes could undergo substantial changes in relatively short periods, shifting by tens of degrees within only a few decades.
“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,” said Yan.
What the James Webb Space Telescope Might Reveal
The James Webb Space Telescope (JWST) has captured high-resolution infrared images of Uranus and Neptune, which scientists are currently analyzing.
Researchers might better understand whether the magnetic poles have moved since Voyager 2’s 1980s flybys by tracking alterations in the visual characteristics of these bright atmospheric phenomena.
“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, professor at Northumbria University who led the JWST observation campaign and reviewed the paper for the journal.
Funding for the study was provided by the National Aeronautics and Space Administration (NASA), the Science and Technology Facilities Council, and The University of Texas Institute for Geophysics (UTIG) housed within the Jackson School of Geosciences.
