The virtually identical oxygen isotope compositions of the Earth and Moon revealed by Apollo return samples have been a challenging constraint for lunar formation models. For a giant impact scenario to explain this observation, either the precursors to the Earth and Moon had identical oxygen isotope values or extensive homogenization of the two bodies occurred following the impact event. Here we present high-precision oxygen isotope analyses of a range of lunar lithologies and show that the Earth and Moon in fact have distinctly different oxygen isotope compositions. Oxygen isotope values of lunar samples correlate with lithology, and we propose that the differences can be explained by mixing between isotopically light vapour, generated by the impact, and the outermost portion of the early lunar magma ocean. Our data suggest that samples derived from the deep lunar mantle, which are isotopically heavy compared to Earth, have isotopic compositions that are most representative of the proto-lunar impactor ‘Theia’. Our findings imply that the distinct oxygen isotope compositions of Theia and Earth were not completely homogenized by the Moon-forming impact, thus providing quantitative evidence that Theia could have formed farther from the Sun than did Earth.

阿波罗返回样本揭示的地球和月球几乎相同的氧同位素组成一直是月球形成模型的挑战性约束。为了用一个巨大的撞击场景来解释这一现象，撞击事件发生后，地球和月球的前兆具有相同的氧同位素值，或者两个物体发生了广泛的均质化。在这里，我们对一系列月球岩性进行了高精度的氧同位素分析，结果表明地球和月球实际上具有明显不同的氧同位素组成。月球样品的氧同位素值与岩性相关，我们建议可以通过撞击产生的同位素轻蒸气与月球早期岩浆海洋的最外层之间的混合来解释差异。我们的数据表明，与地球相比同位素深的月球深部样品具有最能代表原月球撞击物“ Theia”的同位素组成。我们的发现表明，Theia和地球的独特氧同位素组成并未因形成月球的撞击而完全同质化，因此提供了定量证据，证明Theia可能比地球更远离太阳。