Was the Moon-Forming Protoplanet 'Theia' a Neighbor of Earth?

Theia crashed into earth and formed the moon, the theory goes. But then where did Theia come from? The lead author on a new study says 'The most convincing scenario is that most of the building blocks of Earth and Theia originated in the inner Solar System. Earth and Theia are likely to have been neighbors.'

Though Theia was completely destroyed in the collision, scientists from the Max Planck Institute for Solar System Research led a team that was able to measure the ratio of tell-tale isotopes in Earth and Moon rocks, Euronews explains:

The research team used rocks collected on Earth and samples brought back from the lunar surface by Apollo astronauts to examine their isotopes. These isotopes act like chemical fingerprints. Scientists already knew that Earth and Moon rocks are almost identical in their metal isotope ratios. That similarity, however, has made it hard to learn much about Theia, because it has been difficult to separate material from early Earth and material from the impactor.

The new research attempts a kind of planetary reverse engineering. By examining isotopes of iron, chromium, zirconium and molybdenum, the team modelled hundreds of possible scenarios for the early Earth and Theia, testing which combinations could produce the isotope signatures seen today. Because materials closer to the Sun formed under different temperatures and conditions than those further out, those isotopes exist in slightly different patterns in different regions of the Solar System.

By comparing these patterns, researchers concluded that Theia most likely originated in the inner Solar System, even closer to the Sun than the early Earth.



The team published their findings in the journal Science. Its title? 'The Moon-forming impactor Theia originated from the inner Solar System.'

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