History of the Lunar Magnetic Field from Crustal Anomalies

The crust of the Moon possesses magnetic anomalies, which are thought to have been acquired as natural remnant magnetization due to a core dynamo. The field generated in a liquid iron layer in early lunar history, is thought to decay to a halt as the core cooled. The current crustal anomalies therefore may be used to constrain the timing and duration of such a dynamo, which themselves place constraints on the geophysical and thermal evolution of the early Moon. Here, we use crater density as a measurement of crustal age and present correlations between the magnetic anomalies measured from orbit and Absolute Model Ages obtained from crater counts, and with crustal history inferred from geological mapping. The data indicate the dynamo consisted of distinct episodes over lunar history, over at least three distinct epochs. Further fluctuations in the field strength are suggested, motivating the acquisition of additional data.