Terrestrial planets

Out of four terrestrial planets in the solar system – Mercury , Venus, Earth and Mars (left to right, above) – only Mercury and Earth have a dipole magnetic field. Earth's magnetic field is thought to be primarily due to swirling molten iron in the core producing a magnetic field via dynamo action. However, Mercury's field, until now, has been somewhat more of a mystery, because physicists had thought the small planet would have been unable to contain its inner heat so as to keep its core molten. Now, Jean-Luc Margot of Cornell University and physicists from other US and Russian institutions have used complex techniques to interpret radio telescope data – showing that Mercury does indeed have a molten core, probably as a result of alloyed sulfur reducing the melting temperature. (Image courtesy: NASA)

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