Scientists long believed Theia vanished billions of years ago, leaving no chemical trail.
Researchers in France, Germany, and the United States now analyse ancient lunar and terrestrial rocks to trace its birthplace.
They propose that a lost planet that helped create the Moon likely formed much nearer to the Sun than earlier theories suggested.
They reveal that Theia, the body thought to have shaped the Moon, most likely emerged from the inner Solar System.
Experts have upheld the idea for decades that Theia struck the young Earth about 4.5 billion years ago.
That violent collision produced debris that eventually formed the Moon, with fragments of Theia settling in both worlds.
Scientists have discussed the giant impact theory since researchers first studied Apollo samples more than 50 years ago.
Theia’s disappearance left no direct chemistry to confirm the hypothesis, making its identity difficult to define.
A multinational research team now uses aged Moon rocks and Earth samples to examine the ancient planet’s origins.
Jake Foster of the Royal Observatory Greenwich says the work helps reconstruct events that shaped early Earth.
He notes that researchers can pinpoint Theia’s origin despite the planet vanishing 4.5 billion years ago.
Rebuilding a Lost Planet’s Signature
The team studies rocks from Earth and samples returned by Apollo missions to measure their isotopes.
These isotopes act as chemical fingerprints that reveal formation conditions.
Scientists already know Earth and Moon rocks share nearly identical metal isotope ratios.
That resemblance makes it hard to separate early Earth material from debris carried by Theia.
Researchers attempt a planetary reconstruction to understand how the impactor contributed to both bodies.
They analyse isotopes of iron, chromium, zirconium, and molybdenum across hundreds of simulated scenarios.
These scenarios model how early Earth and Theia could produce the isotope patterns seen today.
Material near the Sun formed under different conditions than material farther out, shaping isotope distributions.
Researchers compare these variations to determine Theia’s likely birthplace.
They conclude that Theia probably formed in the inner Solar System, even closer to the Sun than early Earth.
Earlier theories often placed Theia farther from the Sun than Earth.
New Insights into Planetary Origins
Scientists believe this analysis strengthens future studies of planetary growth and early solar system evolution.
They hope the findings will refine how researchers understand collisions, accretion, and the chaotic birth of planets.
The work suggests that dramatic early impacts involved bodies that formed nearer to the Sun than previously assumed.
Researchers anticipate that continued isotope comparisons will reveal more about the vanished world that shaped our own.
