Overview
- The Science paper led by Timo Hopp and Thorsten Kleine measured high‑resolution iron isotopes in 15 Earth rocks, six Apollo lunar samples and 20 meteorites, then integrated other element isotopes into models.
- Earth and Moon materials are nearly indistinguishable in iron isotopes and align with non‑carbonaceous, inner‑solar‑system meteorites rather than outer‑solar‑system sources.
- The modeling best fits a scenario where Theia and proto‑Earth formed from the same inner‑solar‑nebula reservoir, with Theia probably orbiting just inside Earth’s path.
- Results also constrain Theia’s size to be not much smaller than assumed in standard giant‑impact models, while small molybdenum‑isotope offsets tentatively point to a slightly more sunward origin.
- The authors note that extensive post‑impact mixing or a Moon derived largely from vaporized Earth remain viable alternatives, and one report suggests much of Earth’s iron could have been delivered by Theia.