Planetary Magnetic Fields as Tests for Dynamo Mechanisms

Planetary Magnetic Fields as Tests for Dynamo Mechanisms 

The absence of a strong field on Venus, despite its otherwise terrestrial bulk properties, is probably consistent with the dynamo mechanism. The planet rotates about a factor of 250 times more slowly than Earth. Mercury rotates slowly and is too small to support a strong convective core, but it does have a very detectable dipole moment of 2.4 X 10 G cm. Its field is very small, about 0.002 G, and is nearly aligned and probably a relic from the earlier stages of planetary evolution. Mars rotates with nearly the same period as Earth, but it is smaller and may only support a very small convective core. Mars has displayed vulcanic activity in the past, evidence for core or mantle convection, but the planet does not possess even a very weak intrinsic magnetic field. 

Polarity reversals were observed in the sun in the first decades of the twentieth cenmry, long before they were recognized in the earth. The explanation for the reversal of the terrestrial field, therefore, lends support to the dynamo 

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E. Planetary Magnetic Fields as Tests for Dynamo Mechanisms... 

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