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.
38 Articles
38 Articles
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.
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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…
Theia and Earth were neighbors, new research suggests
About 4.5 billion years ago, the most momentous event in the history of Earth occurred: a huge celestial body called Theia collided with the young Earth. How the collision unfolded and what exactly happened afterward has not been conclusively clarified. What is certain, however, is that the size, composition, and orbit of Earth changed as a result—and that the impact marked the birth of our constant companion in space, the moon.
A missing planet called Theia, which is believed to have hit the Earth over 4.5 billion years ago and went to the formation of the Moon, would have come from the inner area of the Solar System, much closer to the Sun than is estimated. New data obtained from the analysis of the moon's rocks and earthquakes suggest that the processes through which the planets are formed could be different from the hypotheses that have so far been accepted.
New Research Suggest Earth and Theia were Neighbors Before They Collided
About 4.5 billion years ago, the most momentous event in the history of Earth occurred: a huge celestial body called Theia collided with the young Earth. How the collision unfolded and what exactly happened afterward has not been conclusively clarified. What is certain, however, is that the size, composition, and orbit of Earth changed as a result—and that the impact marked the birth of our constant companion in space, the moon.
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