Reports

The nature of the lunar crust provides crucial information on the Moon’s origin and subsequent evolution. Because the crust is composed largely of anorthositic materials (1), its average thickness is key to determining the bulk silicate composition of the Moon (2, 3), and consequently, whether the Moon was derived largely from Earth materials or from the giant impactor that is believed to have formed the Earth-Moon system (4, 5). Following formation, the crust of the Moon suffered the conse-quences of 4.5 billion years of impact cratering. The Moon is the nearest and most accessible planetary body to study the largest of these cata-strophic events, which were common during early solar system evolution (6, 7). In addition, it is an ideal laboratory for investigating the cumula-tive effects of the more frequent smaller impact events. Spatial variations in the Moon’s gravity field are reflective of subsurface density varia-tions, and the high-resolution measurements provided by NASA’s Gravi-ty Recovery and Interior Laboratory (GRAIL) mission (8) ar