Magnetic evidence concerning a lunar core

Two different methods were used to determine the lunar electromagnetic response: (1) comparison of Apollo 12 and Explorer 35 magnetometer data; and (2) observation of the dipole field configuration by orbiting Apollo 15 and 16 subsatellites. The methods give significantly different results. The subsatellite observations require the existence of a core, while the Apollo 12 and Explorer magnetometer measurements allow, but do not require, the existence of a core. Despite this, an upper limit of 580 km has been computed for the radius of the core.