Big leap into Neptune’s magnetic field

By combining 26-year old data with supercomputer simulations, scientists have modelled Neptune’s magnetic field in detail.

Astronomers at Imperial College London used the data from Voyager 2 and discovered that Neptune’s magnetic field is perpetually changing and rotating on a different axis to the planet.

Planetary scientist at the Imperial College, Dr Adam Masters said: “Magnetic fields are tricky to understand, even when they are in simple systems. But Neptune is particularly badly behaved. Its odd properties challenge our basic ideas on how magnetospheres work. The planet’s unique magnetic field is still very poorly understood, and our new modelling represents a big leap forward.”

In 1989, Voyager 2 revealed that the planet’s rotation axis is tilted relative to the Sun, its magnetic axis is not at all aligned with its rotation and its magnetic field has a lopsided shape.

“Imagine taking the Earth, tipping it over diagonally, and then moving its magnetic north pole to central Europe, and you start to get a sense of what Neptune is like,” said Dr Masters.

[caption id="attachment_47651" align="aligncenter" width="400"] Neptune as observed by Voyager 2 during its flyby in 1989. Credit: NASA / JPL[/caption]

The team studied the interaction between Neptune’s magnetic field and the solar wind – a stream of charged particles, or plasma – emitted by the Sun. Then, they constructed a magnetic field model of the entire planet by creating a simulation that modelled the result of this interaction, using the Science and Technology Facilities Council’s DiRAC supercomputer.

Dr Masters said: “Modelling a whole planet is no easy task. But supercomputers now make it possible and the new simulations explain a lot of what Voyager saw all those years ago. We can now see how the solar wind enters and circulates around Neptune’s magnetic field. The combination of the dramatic planetary rotation and this circulation pattern is why Voyager 2 found a ‘lopsided’ magnetosphere.”

The team hopes that this model will help astronomers understand planets outside our solar system and improve their ability to forecast space weather events such as geomagnetic storms.

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