New findings challenge long-held theories on the Moon’s birth

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For decades, the prevailing explanation about how the Moon was formed has been the giant-impact hypothesis: the theory that a Mars-sized body called Theia collided with the early Earth some 4.5 billion years ago. Scientists believed this tremendous collision scattered debris throughout space that eventually came together to form the Moon, also shaping the mass and internal composition of Earth.

Now, however, scientists at the Max Planck Institute for Solar System Research (MPS) have presented new evidence in a study released in the journal Science, calling into question the long-held assumptions behind this fantastic cosmic collision. The findings were also discussed in reporting by the New York Post.

According to new research, the Earth-Theia collision may not have been the random encounter it had long been assumed to be. Instead, scientists suggest the two bodies might have formed side by side in the inner Solar System, making them literally neighbours before their fateful impact.

"The most convincing scenario is that most of the building blocks of Earth and Theia originated in the inner Solar System," Timo Hopp, a geoscientist with MPS and the University of Chicago, explained in an interview cited by Universe Today. This suggests a more interwoven early history between the two planetary bodies, one that complicates decades of theories placing the origins of Theia farther afield.

One of the key lines of evidence relates to Earth's iron content. Much of Earth's iron sank into its core early in the planet's history, but not all of it did; the mantle retains more iron than it should. Researchers suggest that this excess mantle iron could only have come from elsewhere, in a situation where Theia contributed a large amount of material-possibly similar in composition because both bodies came from the same region:

Thorsten Kleine of MPS observed that the chemical composition of planetary bodies serves like a "record of their formation," thus helping scientists trace where exactly in the Solar System they hailed from. The new findings suggest Earth and Theia may have been made from the same primordial materials, making the Moon's birth more of an evolutionary step than the product of a random catastrophe.

Not all experts are convinced, however. Dr. Paul Byrne of Washington University in St. Louis told the New York Times, “They've certainly done a lot of work, taking a smorgasbord of samples and trying to make sense of it all. The past really is lost to us.”

Even though scepticism remains, the findings have sparked new debate on one of the most fundamental events to have occurred in the Solar System. If these findings hold, they may reshape the way scientists view how planetary bodies form, evolve, and interact-possibly showing that Earth and its Moon could have been companions long before their collision.