Astronomers discovered Theia, the planet that helped form the Moon, likely formed closer to the Sun than Earth.
For billions of years, scientists lacked direct chemical evidence to trace Theia’s origin.
The giant impact theory proposes Theia collided with early Earth about 4.5 billion years ago.
Debris from that collision coalesced into the Moon, incorporating material from both Earth and Theia.
The theory has guided lunar science since Apollo astronauts returned the first rock samples.
Researchers in France, Germany, and the United States analyzed ancient lunar and terrestrial rocks to identify Theia’s source.
Jake Foster of the Royal Observatory Greenwich said the study almost precisely traces Theia’s birthplace despite its disappearance.
He emphasized that a planet vaporized 4.5 billion years ago can still reveal its history.
Planetary Reverse Engineering
The research team studied Earth rocks and Apollo lunar samples to examine isotopes as chemical fingerprints.
Earth and Moon rocks share nearly identical metal isotope ratios, complicating the isolation of Theia’s material.
Researchers examined isotopes of iron, chromium, zirconium, and molybdenum to model early Earth–Theia scenarios.
They tested hundreds of combinations to determine which produced the isotopic signatures observed today.
Materials forming closer to the Sun experienced different temperatures, creating distinct isotopic patterns across the Solar System.
Comparing these patterns allowed scientists to conclude Theia formed in the inner Solar System, nearer the Sun than Earth.
Earlier hypotheses suggested Theia might have formed farther out, but new evidence challenges that view.
Insights for Planetary Evolution
Researchers hope this analysis advances understanding of how planets grow, collide, and evolve.
The study provides a framework for reconstructing early Solar System dynamics.
It demonstrates how isotopic evidence can reveal vanished worlds and their formation environments.
Astronomers expect future studies to refine models of planetary collisions and Moon formation.
Tracing Theia’s origins helps explain the distribution of materials in the early Earth–Moon system.
This research highlights how ancient rocks preserve the chemical story of Solar System evolution.
Scientists believe similar approaches could reveal the histories of other lost planets and planetesimals.
