Overview
- Researchers from the Max Planck Institute for Solar System Research and the University of Chicago report in Science that Theia most likely formed interior to Earth’s orbit.
- The team measured iron isotopes with record precision in 15 terrestrial samples and six Apollo lunar samples, finding Earth–Moon iron signatures indistinguishable after correcting for cosmic‑ray effects on lunar rocks.
- Reverse modeling that combined iron with chromium, molybdenum, and zirconium constraints produced best‑fit scenarios placing Earth and Theia as close neighbors in the inner Solar System.
- The inferred composition of Theia does not match known meteorite groups, pointing to an unsampled reservoir closer to the Sun than the material that predominantly built Earth.
- The study proposes that iron now present in Earth’s mantle arrived after core formation, possibly delivered by Theia, while outside experts caution that uncertainties in impact mixing, mass partitioning, and limited samples mean further tests are needed.