Some Unsolved Questions about the Early Differentiation of the Moon

The analyses of returned samples and data from in situ and remote sensing observations have substantially advanced our understanding of the lunar internal structure since the Apollo era. Previous studies have confirmed that the Moon resembles a terrestrial planet with a layered core–mantle–crust structure, which formed in the early lunar differentiation initialized by a magma ocean. The important results on the early differentiation of the Moon derived from the ongoing analyses of lunar samples and geophysical data, and experimental studies with different initial conditions, are reviewed in this study. The outstanding problems in the early lunar differentiation, including the formation of the lunar anorthositic crust, the origin of lunar dichotomy, lunar mantle convection, the lunar interior interface, and the chronology of early differentiation, are highlighted and summarized. These unsolved questions may provide research directions for future studies of early differentiation of the Moon. The upcoming lunar exploration missions will return new samples and geophysical data. Comprehensive analyses of the returned samples and the geophysical data (seismology, gravity and topography, and crustal magnetic field), coupled with experimental studies, could provide important results to answer the unsolved questions and constrain the early lunar differentiation.