Overview
- High-precision iron measurements show Earth and Moon are nearly indistinguishable, based on 15 terrestrial rocks and six Apollo samples.
- Comparisons with 20 meteorites indicate both bodies’ building blocks came from the inner solar system rather than distant, carbon-rich regions.
- Reverse-engineering models that match today’s isotopic signatures favor Theia forming slightly closer to the Sun than the proto-Earth, possibly just inside Earth’s orbit.
- The multi-element constraints using iron, chromium, molybdenum and zirconium narrow acceptable collision and mixing scenarios but do not single out one definitive pathway.
- The Science paper by Hopp et al. also allows that part of the iron now in Earth’s mantle was added after core formation by Theia, with key molybdenum signals still requiring confirmation.