Moon scientists long searched for Theia’s chemical signature but found none because the planet vanished billions ago.
A research group in France, Germany, and the United States analysed ancient lunar and terrestrial rocks to track Theia’s birthplace.
They concluded that a long-lost planet involved in the Moon’s creation likely formed much nearer to the Sun than many expected.
Researchers now state that Theia, the body believed to have shaped the Moon, probably emerged from the inner Solar System.
For decades, experts supported the idea that Theia struck early Earth about 4.5 billion years ago.
The collision scattered debris that formed the Moon and left Theia’s material inside both worlds.
Scientists have discussed this giant impact explanation since Apollo missions returned their first geological samples more than 50 years ago.
Theia’s disappearance left researchers without direct chemical proof, complicating efforts to determine its makeup and origin.
The international team used ancient Earth rocks and Apollo samples to uncover Theia’s likely starting point.
Astronomer Jake Foster called the findings remarkable because they help reconstruct events from Earth’s earliest era.
He said researchers can now identify Theia’s origin with surprising precision despite the planet’s total destruction.
Rebuilding a Planet from Rock Clues
The team examined isotopes inside Earth rocks and samples returned from the lunar surface.
These isotopes act as chemical markers that reveal how materials formed under ancient conditions.
Experts already knew that Earth and Moon rocks share almost identical metal isotope ratios.
That similarity made it hard to uncover information about Theia because researchers struggled to separate its material from early Earth’s material.
The new project attempted a detailed form of planetary reconstruction.
Scientists modelled hundreds of potential early-Solar-System conditions using iron, chromium, zirconium and molybdenum isotopes.
They tested scenarios that could produce the isotope signatures found today.
Materials nearer the Sun formed in different temperatures and environments than material farther away.
These conditions created distinct isotope patterns across the Solar System.
A New Picture of the Early Solar System
Researchers compared those patterns and concluded that Theia most likely arose in the inner Solar System.
They determined that Theia formed even closer to the Sun than early Earth, contradicting older theories that placed it farther out.
The study offers a new perspective on how growing planets migrate and collide during their formation.
Scientists hope this analysis will support future work on the evolution of young solar systems and the forces that shape emerging worlds.
