New isotope evidence on the Moon’s origin ^{CEFR B2}

The origin of the Moon matters because it shaped Earth’s early environment. A new multi-institution study finds that the object that struck early Earth—called Theia—probably formed closer to the Sun than Earth did. The work, published in Science, was led by researchers at the University of Chicago, the Max Planck Institute for Solar System Research and the University of Hong Kong.

The team used isotopes—small variations of elements that serve as fingerprints for where material formed in the early solar system. They made precision measurements of iron and combined them with earlier isotope data for chromium, calcium, titanium, molybdenum and zirconium from terrestrial rocks, six lunar samples returned by the Apollo missions, and meteorites from different solar system regions. Their laboratory develops techniques to measure these tiny differences with great precision.

Models of metal movement during planet formation showed that much of early Earth’s iron and molybdenum likely sank to the core before the impact. That implies a significant fraction of iron now in Earth’s crust and mantle may have come from Theia. Simulations testing different Theia compositions indicate the best isotopic match comes from meteorites that formed in regions nearer the Sun. As a result, the authors conclude Earth and Theia were likely neighbors, and the Moon’s stabilizing effect on Earth’s tilt was a fortunate outcome for complex life. Funding came from NASA, the National Science Foundation, the US Department of Energy, Deutsche Forschungsgemeinschaft and the European Research Council.