Does the Moon have the same chemical composition as the Earth's upper mantle?

If the Moon were derived from the Earth, then it is possible that the bulk silicate portions of the Earth and Moon have similar chemical compositions. We have used a combined geophysical and geochemical study to investigate this possibility. Models for the internal structure and internal temperature of the Moon have been combined with a terrestrial upper mantle composition and used to calculate the Moon's density and moment of inertia. These calculated values are then compared to measured values to evaluate whether the bulk silicate Moon could have the same composition as the Earth's upper mantle. Only a very restricted set of parameters allows the upper mantle composition to simultaneously meet the geophysical constraints of density and moment of inertia. In particular, if the Moon has the composition of the Earth's mantle, then the Moon must have a rather large core (≃500 km radius). If the Moon had a core of such size and if the Moon's siderophile element abundances were initially those of the terrestrial upper mantle, then siderophile elements should be much more depleted in lunar materials than is observed. -Authors