Impactor origins key to Moon's similarity to Earth

The Moon is thought to have formed mainly from material within a giant impactor that struck the proto-Earth, so it seems odd that the compositions of the Moon and Earth are so similar, given the differing composition of other Solar System bodies. Alessandra Mastrobuono-Battisti et al. track the feeding zones of growing planets in a suite of computational simulations of planetary accretion and find that different planets formed in the same simulation have distinct compositions, but the compositions of giant impactors are more similar to the planets they impact. A significant fraction of planet–impactor pairs have virtually identical compositions. The authors conclude that the similarity in composition between the Earth and Moon could be a natural consequence of a late giant impact.