Space Station Info >> Magnetosphere

Magnetosphere

Mercury has a relatively strong magnetosphere, with 1% of the magnetic field strength generated by Earth. It is possible that this magnetic field is generated in a manner similar to Earth's, by a dynamo of circulating liquid core material, though scientists are unsure whether Mercury's core could still be liquid, although it could perhaps be kept liquid by tidal effects during periods of high orbital eccentricity.

Mercury has a higher iron content than any other solar system object. Several theories have been proposed to explain Mercury's high metallicity. One theory is that Mercury originally had a metal-silicate ratio similar to common chondrite meteors and a mass approximately 2.25 times its current mass, but that early in the solar system's history Mercury was struck by a planetesimal of approximately 1/6 that mass. The impact would have stripped away much of the original crust and mantle, leaving the core behind. A similar theory has been proposed to explain the formation of Earth's Moon; see giant impact theory.

Alternatively, Mercury may have formed from the solar nebula before the Sun's energy output had stabilized. The planet would initially have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2500–3500 K; and possibly even as high as 10000 K. Much of Mercury's surface rock would have vaporized at such temperatures, forming an atmosphere of "rock vapor" which would have been carried away by the solar wind.

A third theory suggests that the solar nebula caused drag on the particles from which Mercury was accreting, which meant that lighter particles were lost from the accreting material. Each of these theories predicts a different surface composition, and so one of the aims of the forthcoming MESSENGER mission to the planet is to take observations that will allow the theories to be tested.