EARTH
In the literature: open
Was the Moon-forming impactor isotopically Earth-like?
In plain words
The isotope puzzle disappears if the impactor formed in the same neighborhood of the solar system as Earth. Whether that is plausible depends on where the planets' building blocks came from.
Precise statement
Determine whether the impactor (Theia) formed from the same isotopic reservoir as the proto-Earth, for example an enstatite-chondrite-like inner-disk source, so that the Earth-Moon match follows without mixing. An answer is a probability, from planet-formation models calibrated on meteorite isotope anomalies (O, Ti, Cr, Mo, Zr), that two such embryos share isotopes within measured limits.
What would settle it
N-body formation models with isotopic tracking compared to the measured Earth-Moon differences.
Related problems
- Special case of Why are Earth and Moon isotopically nearly identical?