The Magnetism of the Planets


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           The Earth has a magnetic field. Its magnetic field is just like a bar magnet. A compass lines up with the magnetic field of the earth. The magnetic field has a north and a south pole. It is called a dipole field.

           The north magnetic pole is located just off the coast of Antarctica. The magnetic field is tilted 11 degrees from the spin axis. The north pole of a compass needle is a magnetic north pole. It is attracted to the geographic North Pole, which is a magnetic south pole (opposite magnetic poles attract).

           Circulating electric currents in the Earth's molten metallic core are the origin of the magnetic field. And the Earth's magnetic field can be attributed to a dynamo effect of circulating electric current, but it is not constant in direction. Rock specimens of different age in similar locations have different directions of permanent magnetization. However, the details of the dynamo effect are not known in detail. The rotation of the Earth plays a part in generating the currents which are presumed to be the source of the magnetic field. However, Venus does not have such a magnetic field although its core iron content must be similar to that of the Earth. Venus's rotation period is just too slow to produce the dynamo effect. All planets with strong magnetic fields rotate rapidly (at least once every few earth days) and also contain an electrically conducting liquid like that of Earth.