Space Science Reviews,
Vol. 111, Iss. 1, pp. 1-32, doi: 10.1023/B:SPAC.0000032719.40094.1d, March 2004.
Figure 4: Mean square amplitude of the magnetic field on the surface of a sphere (radius a) from spherical harmonics of degree n for Earth (a = 6371 km) and Mars (a = 3394 km). The fitted curve for the Earth is the sum of spectra from core sources (dynamo) and that of a crustal source shell of random dipoles at shallow depth. The fitted curve for Mars is that of a source shell of random dipoles in the crust only (after Voorhies et al., 2002).