High Quality Content by WIKIPEDIA articles! Mercury`s magnetic field is approximately a magnetic dipole (meaning the field has only two magnetic poles) that is significant, and apparently global, on planet Mercury. Data from Mariner 10 led to its discovery in 1974; the spacecraft measured the field`s strength as 1.1% that of Earth`s magnetic field. The origin of the magnetic field can be explained by dynamo theory, and because the magnetic field is strong enough near the bow shock, it slows down the solar wind, which induces a magnetosphere.