Computer simulations show that changing electrical conductivity deep inside Uranus and Neptune can explain their heavily tilted and distorted magnetic fields. Researchers published these findings on November 3 in the Communications Physics journal, suggesting that the ice giants’ magnetic poles might shift dramatically over just a few decades.
Voyager 2 Discoveries at the Ice Giants
When NASA’s Voyager 2 spacecraft flew past Uranus in January 1986 and Neptune in August 1989, it revealed planetary magnetic fields unlike anything else in the solar system, Space reported. Earth features a relatively orderly magnetic field aligned closely with its rotation axis. In sharp contrast, the ice giants possess dramatically tilted and asymmetric magnetic fields. Uranus has a magnetic dipole tilted by 59 degrees, while Neptune’s dipole is tilted by 47 degrees.
Earth’s magnetic field generates through a dynamo process where circulating liquid iron in the outer core creates a bar-magnet effect. Universe Today said that Uranus and Neptune also drive strong dynamos, but their fields show severe disarray and multi-peaked properties. Scientists call the lopsided components of these fields M-1 peaks, which dominate the magnetic strength of the ice giants in stark contrast to Earth and Jupiter.
Simulations Reveal How Internal Composition Affects Planetary Dynamos
Researchers at The University of Texas at Austin, alongside teams from the University of California, Los Angeles, Imperial College London, and Northumbria University, investigated what drives these anomalies. They developed computer simulations testing how internal composition and temperature affect dynamo processes.
“Deep inside Uranus and Neptune, pressures and temperatures become extremely high,” said Chi Yan, a research associate at the UT Jackson School of Geosciences, in an interview with Science Daily.
“Under these conditions, which can cause water molecules to break apart into ions, the material may become increasingly electrically conductive with depth.”
Yan said that these ice giants are roughly four times wider than Earth and consist largely of hydrogen, helium, water, ammonia, methane, and rocky material. The new models demonstrate that as electrical conductivity increases deeper inside the planets, circulating fluids generate the observed distorted magnetic fields.
Rapid Decadal Shifts in Magnetic Tilts
The computer models indicate that the magnetic fields of Uranus and Neptune are far less stable than Earth’s magnetic field, which drifts by only a degree or so over half a century.
“Our models show the ice giants can behave very differently,” Yan told Science Daily.
“In some stretches the tilt swings by tens of degrees within decades. In others it shifts only slightly over the same span.”
This rapid variability means the magnetic configuration surrounding both planets today may differ substantially from the snapshot recorded by Voyager 2 four decades ago.
Testing Models With the James Webb Space Telescope
Scientists are currently analyzing infrared images captured by the James Webb Space Telescope to search for evidence of these rapid magnetic changes. Researchers are focusing on the planets’ auroras, which glow when charged particles from the Sun interact with atmospheric gases in the ionosphere.
“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 observation campaign.
The research was funded by The University of Texas Institute for Geophysics in the Jackson School of Geosciences, NASA, and the Science and Technology Facilities Council, according to Science Daily.
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