Mercury's magnetic field

Focus on Mercury: The Messenger space probe - which took this image - has confirmed that the innermost planet has a magnetic field 150 times weaker than that of Earth. Researchers have now found an explanation for this. © NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Mercury, the smallest of the eight planets with a diameter of 4900 kilometres and the closest to the Sun, looks more like the Moon than the Earth from the outside. It is the only rocky planet that has a global magnetic field like Earth. But why is its magnetic field so much weaker than Earth’s? Scientists at the Technische Universität Braunschweig and the Max Planck Institute for Solar System Research have now presented a new explanation: the solar wind counteracts Mercury’s internal dynamo and thus weakens its magnetic field. more here