Internal structure of the Moon

The Moon has a rocky crust, a thick silicate mantle, and a small metallic core. Their dimensions and physical states are inferred from seismic, gravitational, magnetic, and laboratory evidence.

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Lunar seismology: The study of seismic waves recorded on the Moon to investigate its interior and seismic activity. Apollo seismometers supplied the direct wave evidence used to infer deep boundaries.
Lunar crust: The Moon’s outermost solid layer, composed mainly of anorthositic highlands and basaltic surface regions. Its thickness varies across the Moon and records early crust formation.
Giant-impact hypothesis: The leading model that the Moon formed from debris produced by a giant collision with the early Earth. It frames the Moon’s initial composition and thermal state.
Lunar seismometer network: A distributed set of lunar seismometers designed to record seismic waves across multiple locations. A modern network could resolve interior boundaries that Apollo’s sparse stations could not.
Apollo Lunar Surface Experiments Package: A suite of scientific instruments deployed by Apollo astronauts at several lunar landing sites. Its seismometers recorded the moonquakes that constrain the interior.
Lunar mantle: The thick silicate layer between the lunar crust and core. Its composition and temperature govern much of the Moon’s interior structure.
Lunar differentiation: The separation of the Moon’s materials into compositionally distinct layers during its evolution. It is the process that produced the crust, mantle, and metallic core.
Lunar core crystallization: The freezing and compositional evolution of the Moon’s metallic core over time. Its history may explain magnetic evidence and the core’s present physical state.
Lunar gravity field: The spatial variation in the Moon’s gravitational acceleration, shaped by its mass distribution and rotation. Gravity measurements reveal mass concentrations and constrain interior density.
Lunar core: The Moon’s small central region, thought to include an iron-rich metallic component. Seismic, rotational, and magnetic evidence constrain its layered structure.