US EditionStudy Finds Moon-Forming Impactor Theia Originated Near Earth
High-precision isotope analysis shows Theia formed closer to the Sun than Earth, explaining their near-identical compositions and supporting the inner Solar System origin theory.
- On Nov. 20, 2025, a study in Science led by Timo Hopp of the Max Planck Institute and University of Chicago concluded Theia originated in the inner Solar System, closer to the Sun than proto‑Earth.
- Isotopic measurements showed Earth and the Moon have nearly identical signatures, which obscured Theia's origin and sparked debate over whether it formed in the inner or outer Solar System.
- Using high‑precision isotope analyses, the team measured iron, chromium, molybdenum and zirconium isotopes in 15 terrestrial rock samples, six lunar samples returned by Apollo astronauts, and 20 non‑carbonaceous meteorites and combined these with mass‑balance calculations and modeling to back‑calculate Theia's likely composition and origin.
- The research suggests `The most convincing scenario is that most of the building blocks of Earth and Theia originated in the inner Solar System`, clarifying early Solar System architecture and heavy-element delivery, said Timo Hopp.
- Modeling indicates Theia was a rocky planet with a metallic core containing five to ten percent the mass of Earth, impacting proto-Earth over 4.5 billion years ago, with three possible explanations for Earth–Moon similarity.
50 Articles
50 Articles
The Earth once survived the collision with another planet from whose rubble the Moon was formed. Now, researchers conclude that the mysterious planet called Theia has its origin. Meteorite finds also help with this.
Based on chemical clues, they are trying to decipher what kind of protoplanet collided with the Earth and how the Moon was born.
Scientists may have found the planet that made the Moon
About 4.5 billion years ago, a colossal impact between the young Earth and a mysterious planetary body called Theia changed everything—reshaping Earth, forming the Moon, and scattering clues across space rocks. By examining subtle isotopic fingerprints in Earth and Moon samples, scientists have reconstructed Theia’s possible composition and birthplace.
Eurek Alert
Scientific InquirerTheia and Earth were neighbors
In the upcoming issue of the journal Science, researchers determine the possible composition of Theia, the body that collied with Earth 4.5 billion years ago thus creating the Moon. The impactor’s composition allows conclusions about its place of origin. It is located in the inner Solar System, likely closer to the Sun than Earth. Lunar rocks from the Apollo missions were used in the analyses. For the first time, researchers used their rat…
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