The primaeval lunar magnetic field: Its relevance to the interpretation of planetary fields

Abstract The Moon today has no general magnetic field but the remanant magnetization of rocks returned and crustal magnetic fields show that it had one once. Palaeointensity laboratory measurements show the field approached 0.1 mT (1G) 3.9 Ga ago, decreasing exponentially to about 0.002 mT 3.2 Ga ago: evidence for a small iron core dynamo. Palaeomagnetic poles, determined from satellite magnetic surveys, show the Moon to have reorientated several times with respect to its axis of rotation and to have had a primaeval satellite system, the decay of their orbits producing the multi-ring impact basins. I conclude that planetary field strengths vary with evolutionary factors, such as the energy sources for convection; thus doubt is thrown on “scaling laws”.