Abstract
A new scaling law for the planetary magnetism was developed on the assumption that the Lorentz force balances the Coriolis force in the planetary core. In deriving the scaling law we decomposed the vector fields into the toroidal and the poloidal components, and dealt with them separately. From the scaling law, not only we can predict the dipole moments of the planets, but also can we estimate the toroidal magnetic field intensity in the planetary core; the result implies a typical toroidal magnetic field intensity of 100 [G], and the toroidal and the poloidal velocity fields respectively of the orders of 1 x 10-5 [ms-1] and 4 x 10-7 [ms-1] in the Earth's core. Since the present study is based on an αω-dynamo model, the resultant scaling law depends on the efficiency of the α-effect. If we adopt the dependence of the form α ∝ Ω (with Ω the angular velocity of the planet's self-rotation), the magnetic dipole moment M of a planet scales as M ∝ (characteristic length)7/2(mean density)1/2(angular velocity). The predictions agree well with the observations except Venus and Mars.
