2025-11-20 マックス・プランク研究所（MPG）
Artist’s impression of the collision between the early Earth and Theia. Since Theia originated in the inner Solar System, in this perspective the Sun can be seen in the background. © MPS / Mark A. Garlick
＜関連情報＞
- https://www.mpg.de/25743917/theia-and-earth-were-neighbors
- https://www.science.org/doi/10.1126/science.ado0623
月形成衝突体テイアは太陽系内部から発生した The Moon-forming impactor Theia originated from the inner Solar System
Timo Hopp, Nicolas Dauphas, Maud Boyet, Seth A. Jacobson, and Thorsten Kleine
Science Published:20 Nov 2025
DOI:https://doi.org/10.1126/science.ado0623
Editor’s summary
In the early Solar System, a small planet known as Theia collided with proto-Earth. The debris from that giant impact formed the Moon, with material from Theia incorporated into both the Moon and Earth. Hopp et al. measured iron isotopes in lunar samples, Earth samples, and meteorites. They then combined these results with previous measurements of other elements with different geochemical behaviors. By simultaneously calculating the contributions of Theia material to each of those elements in both bodies, the authors concluded that Theia formed in the inner Solar System, nearby to Earth but possibly slightly closer to the Sun. —Keith T. Smith
Abstract
The Moon formed from a giant impact of a planetary body, called Theia, with proto-Earth. It is unknown whether Theia formed in the inner or outer Solar System. We measured iron isotopes in lunar samples, terrestrial rocks, and meteorites representing the isotopic reservoirs from which Theia and proto-Earth might have formed. Earth and the Moon have indistinguishable mass-independent iron isotopic compositions; both define one end of the range measured in meteorites. Combining our results with those for other elements, we performed mass balance calculations for Theia and proto-Earth. We found that all of Theia and most of Earth’s other constituent materials originated from the inner Solar System. Our calculations suggest that Theia might have formed closer to the Sun than Earth did.
