Scientists have finally uncovered a clearer picture of where the mysterious planet Theia came from — the same planet believed to have slammed into Earth about 4.5 billion years ago and helped form the Moon. This new insight comes from researchers at the Max Planck Institute for Physics, who dug deep into the chemical fingerprints hidden in rocks from both Earth and the Moon.
Even though Theia was completely destroyed during that massive cosmic collision, pieces of it are still preserved in the materials we can study today. According to the researchers, the chemical makeup of a planetary body can actually reveal its entire “life story,” including where it was born.
To get these answers, the team analyzed isotopes of iron, chromium, molybdenum, and zirconium found in samples brought back from the Moon and compared them with rocks here on Earth. The results were surprising — the similarities were extremely close. This strongly supports the idea that Earth and Theia came from the same raw materials and shared an early connection in the Solar System.
The researchers didn’t stop there. They used a type of “reverse engineering” method to rebuild what Theia and the early Earth likely looked like in terms of composition.
And here's the plot twist: most of the building blocks of both planets seem to have formed in the inner part of the Solar System. That suggests Earth and Theia were basically neighbors from the start — with Theia sitting even closer to the Sun than Earth did.
This discovery also explains why the Moon’s composition looks almost identical to Earth’s. Since the Moon formed from the debris thrown into space after Theia crashed into Earth, it makes sense that both bodies share the same chemical fingerprints.
Scientists estimate that Theia was roughly the size of Mars. Around 4.5 billion years ago, it hit Earth at an angle. That collision caused their cores to merge, while large chunks of their silicate mantles were blasted into space. Over time, that material came together and formed the Moon we see today.
This new research doesn’t just help us understand how the Moon was born — it also paints a vivid picture of Earth’s earliest days and the dramatic end of its lost planetary neighbor, Theia.
Photo source: CC0 Public Domain
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