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Uranus and Neptune’s tangled magnetic fields find a possible explanation

Computer simulations reproduced features of the ice giants’ unusual magnetic fields by changing how easily electricity flows at different depths. The peer-reviewed study points to interior conductivity as a possible explanation for Voyager 2’s measurements. Some simulated fields also changed over decades, a possibility that matters when interpreting the planets’ aurorae.

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A physical Voyager spacecraft replica in a space-science museum, with its white antenna facing forward and its magnetometer boom extending to the side.

Conductivity changes the field

A new model of Uranus and Neptune links their unusually tangled magnetic fields to differences in electrical conductivity deep inside the planets. The peer-reviewed research announced by the University of Texas at Austin reproduces important features of measurements from the Voyager 2 spacecraft.[1], [2]

The researchers compared three-dimensional simulations with uniform conductivity against ones in which electricity flows more easily at greater depths. Uniform conditions favoured a simpler field arranged around the rotation axis. Conductivity increasing inward instead encouraged off-axis structures and multiple magnetic components. Varying the thickness of the conducting region showed that its geometry and conductivity work together, rather than leaving one thin shell as the only explanation.[1]

Voyager’s single encounters

Voyager 2 passed Uranus in 1986 and Neptune in 1989. Each flyby supplied one direct encounter with a planet’s magnetic field. Unlike a simple two-pole field aligned with planetary spin, the measured fields have substantial additional structure and pronounced tilts. Simulations resembling those observations sometimes changed their orientation or pattern over decades. Those timescales depend on assumed interior properties; the observations do not yet establish how much either real field has changed.[1]

Aurorae offer another view

The possible evolution matters for interpreting aurorae, the emissions observed around the planets’ magnetic regions. A shift in where an aurora appears could reflect changes in the underlying field. Existing positional uncertainties leave that interpretation unresolved. The researchers identify extended auroral monitoring and future spacecraft measurements as ways to separate competing interior models. A new encounter would provide a comparison across time as well as a more detailed description of the field’s shape.[1]

For more information on this topic, you can read the related columns.

References

  1. News sourceCommunications PhysicsInterior conductivity offers an explanation for Uranus and Neptune’s unusual magnetic fields↩1↩2↩3↩4
  2. News sourceUniversity of Texas at AustinConductivity differences may explain the ice giants’ magnetic fields↩
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