Planetary and lunar magnetism

Knowledge on intrinsic planetary magnetic fields is summarized. For the Earth, the spatial configuration and the present and past time variations of the internally generated field are known in detail. Important features are secular changes of nondipole components, of the dipole orientation and strength, and frequent polarity reversals. Today the Moon has no detectable dipole moment, but magnetic field measurements show widespread magnetization of the lunar crust and lunar rocks have strong stable remanent magnetizations, which indicate the presence of magnetic fields between 3 and 4 Gyr ago. The origin of these fields and the magnetizing processes of lunar rocks are not known.