Why do planets have magnetic fields?

How do swirling liquids in a planet’s core help create a protective magnetosphere?


Asked by Andy Barret

Planetary magnetic fields are produced by churning motions of liquids at a planet’s core that conduct electricity and have an electric charge. The magnetic fields act like giant bar magnets and can be offset from the rotation axis of a planet. For example, the Earth’s magnetic field is tilted about 11 degrees to the axis of rotation.

Magnetic fields protect a planet from the charged particles streaming out from the Sun in the form of the solar wind. The particles are deflected outwards by the magnetic field lines. Earth has a strong magnetic field because it has a liquid conducting core composed of iron-nickel that rotates swiftly every 24 hours. In contrast, Mars exhibits only remnants of an ancient magnetic field because the iron core has cooled for unknown reasons and perhaps solidified.

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