MERCURY鈥橲 puny magnetic field may be so weak thanks to constant wrangles with the solar wind.
NASA鈥檚 Mariner 10 mission detected a magnetic field around our solar system鈥檚 innermost planet in 1974, but its cause remained a mystery 鈥� until recent measurements suggested that Mercury鈥檚 core may be partly molten. As with Earth, these 鈥渕oving parts鈥� could act like a dynamo, generating electricity and consequently a magnetic field. But that cannot explain why Mercury鈥檚 field is so weak, says Karl-Heinz Glassmeier at the Institute for Geophysics and Extraterrestrial Physics at Braunschweig, Germany.
The answer may lie at the magnetopause 鈥� the boundary between Mercury鈥檚 magnetic field and the solar wind. Glassmeier鈥檚 calculations show that strong electric currents generated there would create a secondary magnetic field, which 鈥� given the direction of the solar wind 鈥� would oppose the polarity of Mercury鈥檚 own field, weakening it (Geophysical Research Letters, vol 34, p L22201). This doesn鈥檛 happen on Earth as its magnetopause field is too far from the surface to have an effect.
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