Thermal core‐mantle coupling in an early lunar dynamo: Implications for a global magnetic field and magnetosphere of the early Moon

A theoretical model suggests a short‐lived lunar dynamo driven by a mantle overturn forming crustal thickness dichotomy, while the lunar paleomagnetic data and crustal magnetic fields suggest both of presence and absence of a global magnetic field of the Moon ∼4 billion years (Gyr) ago. Here we carry out numerical simulations of a possible lunar dynamo, including effects of mantle overturn on heat flux heterogeneity at the core‐mantle boundary. As a result, the surface field intensity of the lunar dynamo is about 100 nT. In this case, a lunar magnetosphere could be present with a sunward size of 1.4 times the Moon's radius. Considering the 4.6 Gyr orbit evolution of the Moon, the magnetic field intensity and the magnetosphere size could be larger, suggesting the lunar crustal magnetization acquired in the ancient dynamo field.