A new Science journal study by researchers from the Max Planck Institute and the University of Chicago found that Earth and Theia—the planet-sized body that created the moon after a massive collision 4.5 billion years ago—likely formed near each other in the inner solar system. The finding comes from precise isotope analysis of Earth and lunar rocks.

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• Researchers measured iron isotope ratios in Earth and moon rocks with record precision.
• Earth and moon showed identical isotope signatures across multiple metals.
•  Team used “reverse engineering” to model Theia’s size and composition.
•  Models indicate Earth and Theia formed mainly from inner solar system material.
•  Suggests Theia likely orbited closer to the sun than early Earth.
•  Similar isotopes do not reveal exact collision details due to multiple possible scenarios.
•  Elements like iron and molybdenum trace post-core formation material added by Theia.
•  Zirconium isotopes captured Earth’s full formation history, aiding reconstruction.
•  Some meteorite classes match early Earth’s building blocks but not Theia’s.
• Study hints Theia contained previously unknown material not found in meteorites today.