ESA Science & Technology13-Jul-2005 13:50:43

Mercury Interior

Magnetic Field

Mercury is the only terrestrial planet apart from the Earth which has a significant magnetic field (a few 100 nT at the equator, equivalent to about one hundredth that of the Earth). However, little is known about the field's characteristics. It may, for example, be due to a magnetised crust similar to that on Mars. Alternatively, it could be generated by circulation within a molten section of the core, similarly to Earth. This dynamo model implies that the outer core of Mercury is still partially molten and probably contains a small fraction (2-4%) of sulphur. Camera observations of the libration (oscillations of the planet) and other measurements will help to confirm this.

How does the planetary magnetic field interact with the solar wind in the absence of any ionosphere?

The region in space where a planetary magnetic field interacts with the solar wind is called a magnetosphere. Mercury's magnetosphere is only 5% the volume of the Earth's, even though the planetary radii differ by less than a factor of 3. Mercury's magnetosphere is exposed to a solar wind density and an interplanetary magnetic field (IMF) 4 - 9 times larger than Earth's.

Magnetic field, wave and particle measurements will tell us about the similarities and differences between the magnetospheres of Mercury and Earth.

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