Planetary Magnetic Fields : Gas Giants

Ever wondered how the beautiful auroras we see are formed? You are right, it’s due to the energetic particles carried along with the solar wind from the sun, that enter the magnetic field shield, called the magnetosphere of the planet, interacts there and collects at the poles. Why at the poles? Because that’s how the field lines travel. But it doesn’t just happen on Earth. And it doesn’t just emit visible light spectrum, at least on the outer planets.

Interior models of the giant planets. Image : NASA/Lunar and Planetary Institute

The gas and ice giants of our Solar system - Jupiter, Saturn, Uranus and Neptune - have extremely large magnetic fields and magnetospheres. Their interiors are unlike the interior of the terrestrial planets. They are mostly composed of gases and have a small solid core. Their magnetic fields are similar to that of Earth, i.e, dominantly dipolar, but the magnitudes are much larger than the terrestrial value. 

The interiors of Jupiter and Saturn consist of hydrogen and helium in different forms. Jupiter has the largest magnetic field in the Solar system that is assumed to be generated from the metallic hydrogen in its interior. The magnetosphere is so large that its tail almost reaches Saturn. The metallic hydrogen of Saturn is considered smaller in size comparatively and thus produces a lower magnetic field, but still much larger than Earth’s. The dipole magnetic field axis and the rotation axis almost align.

Magnetic field of the outer planets. Image : Stevenson 2018

The ice giants, Uranus and Neptune, have no metallic hydrogen but have molecular hydrogen and compounds like methane and ammonia in their interior. Uranus has an off-centered field. It rotates on its side due to its large tilt and its magnetic and rotation axes make a 59 degrees angle between them. The magnetic field and magnetosphere of Neptune is similar except that the planet is not as tilted.

Read about the magnetic fields of terrestrial planets here.



Shivangi Sharan is a second year PhD student at the Laboratory of Planetology and Geodynamics in France. Her research focusses on the study of the magnetic field of Mars and to infer its internal structure from it. She is an active member of the IAGA Blog Team and can be contacted via e-mail here.



  

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