Around 100 million years after the formation of the solar system, a Mars-sized object dubbed Theia slammed into the Earth and created the Moon. We now have a better idea as to where this wayward object came from.

In a study published today in the journal Science, researchers investigated the isotopic fingerprints —the ratio of isotopes, or versions, of elements in a material—of iron in rocks from the Moon, Earth, and meteorites (meteoroids that reach the ground). Their results bolster the theory that the impactor was born in the inner solar system and closer to the Sun than where Earth originated.

Their findings suggest that Theia—lurking in the inner solar system—eventually drifted outward and collided with the proto-Earth around 4.5 billion years ago, a violent impact that shatte

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