dynamo effect

The dynamo theory explains the origin of Earth's main magnetic field. It proposes that fluid motion within Earth's outer core, composed of liquid iron, generates electric currents. These currents, in turn, produce a magnetic field that aligns with Earth's rotation axis. This self-sustaining process was developed by physicists Walter M. Elsasser and Edward Bullard in the mid-20th century and is the prevailing explanation for the geomagnetic field.1

The principle behind a dynamo is demonstrated by Michael Faraday's invention of the first electric generator. He discovered that moving a magnet near a wire coil, or moving a wire coil near a magnet, could induce an electric current. This concept of electromagnetic induction is fundamental to how dynamos generate electricity.2

Mercury also possesses a magnetic field, similar to Earth's, which is believed to be generated by a dynamo mechanism within its liquid iron core.3