Artwork depicting the young Earth's collision with Theia, with the inner Sun visible behind themScientists used isotopes in Earth and Moon rocks to identify Theia, the planet that formed the Moon. Results suggest it came from closer to the Sun, revealing new clues about the Solar System's early history.
For decades, researchers have agreed on one dramatic origin story for the Moon: billions of years ago, a Mars-sized world -- nicknamed Theia -- smashed into the young Earth. The impact reshaped our planet, threw vast amounts of material into space, and ultimately formed the Moon. Yet one crucial piece has always been missing: What exactly was Theia?
Add Asianet Newsable as a Preferred Source
A new study from the Max Planck Institute for Solar System Research and the University of Chicago, published in Science, may finally offer the most complete picture of this long-lost world. Using extremely subtle chemical clues hidden in both Earth and Moon rocks, scientists have reconstructed Theia's composition and traced its birthplace in the early Solar System.
Chemical Fingerprints Tell an Ancient Story
To track down Theia, researchers turned to isotopes -- slightly different versions of the same chemical element. In the early Solar System, these isotopes formed in uneven patterns, depending on how far a material was from the Sun. That means each region of the Solar System carries its own chemical "accent," preserved inside planets and meteorites.
The research team measured iron isotope ratios in 15 Earth samples and six Apollo lunar samples with unprecedented precision. Earth and Moon rocks were almost indistinguishable, confirming that their materials were heavily mixed during the gigantic collision. But that similarity also made solving the mystery more difficult. If Earth and Theia mixed so thoroughly, how could anyone figure out what Theia looked like before the impact?
Reconstructing a Lost World
To overcome this challenge, the team treated the Earth-Moon system like a puzzle. They tested countless combinations of possible early Earth and Theia compositions to see which scenarios could produce the identical isotope ratios visible today.
They didn't just analyze iron -- they also included chromium, molybdenum, zirconium, and other elements that record different stages of planetary evolution. Some, like molybdenum, trace the formation of a planet's core. Others, like zirconium, reflect the earliest building materials of rocky planets.
Their calculations showed that while Earth's composition can be explained by a mixture of known meteorite types, Theia is a different story. Its chemical signature doesn't match any meteorite groups found today.
Theia Formed Even Closer to the Sun
The models point to a striking conclusion: Theia likely formed even closer to the Sun than Earth did. That would make Earth and Theia close neighbors, built from similar -- but not identical -- solar materials. Eventually, their orbits crossed, leading to the violent collision that forever changed both worlds.
This work brings researchers closer to solving one of planetary science's oldest mysteries. By piecing together chemical clues, they've begun to reveal the identity of the planet that made the Moon -- and helped shape the Earth we know today.
Read Full Article