Scientists long believed Theia struck early Earth, yet they lacked direct chemical proof because Theia vanished billions ago.
Astronomers in France, Germany, and the United States analysed ancient lunar and terrestrial rocks to uncover Theia’s origin.
Researchers now propose that Theia formed much nearer to the Sun than earlier theories suggested.
They argue that this long-lost planet arose in the inner Solar System before colliding with young Earth.
For decades, scientists have supported the giant impact theory to explain the Moon’s creation.
This idea states that debris from the collision produced the Moon and left Theia’s material in both bodies.
Apollo missions supplied samples that helped researchers build this hypothesis over fifty years.
Theia’s disappearance made its composition elusive, preventing direct chemical confirmation.
The new study uses surviving rocks to retrace the ancient planet’s birthplace.
Astronomer Jake Foster praised the findings for locating a planet destroyed 4.5 billion years ago.
He noted that researchers can pinpoint Theia’s origin despite its vaporisation in the early Solar System.
Tracing Chemical Clues
The research team examined Earth rocks and Apollo lunar samples to study their isotopes.
These isotopes act as chemical fingerprints that reveal formation conditions in early space.
Scientists already recognised the near-identical metal isotope ratios in Earth and Moon samples.
That similarity complicated efforts to distinguish early Earth material from pieces of Theia.
The team approached the puzzle through planetary reverse engineering.
They analysed isotopes of iron, chromium, zirconium and molybdenum across numerous models.
They tested hundreds of scenarios to see which combinations matched today’s isotope signatures.
Materials near the Sun formed under different temperatures and therefore hold distinct isotope patterns.
Those variations allowed scientists to compare regions of the Solar System with present-day samples.
Their results indicate that Theia likely emerged in the inner Solar System, closer to the Sun than early Earth.
This challenges earlier ideas that placed Theia farther out in the Solar System.
Understanding Planetary Beginnings
Researchers believe this analysis can deepen knowledge of how planets form, collide and transform during early system development.
They think these findings may guide future studies of planetary growth and early Solar System evolution.
The work demonstrates how scientists can reconstruct vanished worlds using the chemical traces they left behind.
