The Earth and the Moon. The Earth and the Moon. The Earth and the Moon. (Photo: MarcelClemens/Shutterstock)

How was the moon formed? Scientists think they have it figured out

New research supports popular belief that the moon formed after Earth collided with another planet.

A popular hypothesis about how the moon was formed just received a credibility boost. Scientists from France and Israel believe the moon formed from debris after Earth collided with a rock half its size.

The joint study, reported in Nature, supports the Giant Impact Hypothesis, which was first proposed in the 1970s. This theory says the moon formed after a nascent Earth collided with a Mars-sized object called Theia. The moon formed from the debris created by the collision. 

However, this hypothesis has faced challenges. Most bodies in the solar system have unique chemical makeups. But rock samples from the moon show that its makeup is nearly identical to Earth's. 

"In terms of composition, the Earth and moon are almost twins, their compositions differing by at most few parts in a million," the study's lead author, Alessandra Mastrobuono-Battisti, an astrophysicist at the Israel Institute of Technology in Haifa, told "This contradiction has cast a long shadow on the giant-impact model."

The French and Israeli scientists conducted 40 different computer simulations focusing on the birth of our solar system. The scientists determined that three or four large planets survived the violent solar system formation. They learned that, while many of the planets were dissimilar, 20 to 40 percent of the time the composition of one planet was in fact very similar to the makeup of the protoplanet it collided with. This is roughly 10 times greater than previous estimates. 

For more, check out this infographic from 

Conceptual illustrations of the birth of the moon.


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