WASHINGTON (AP) - New research suggests that the Earth may once have had two moons.
In a paper published in the journal Nature, astronomers theorize that the moons were formed about 4.5 billion years ago, when a giant planet smashed into Earth. They would have orbited relatively close together, with the smaller one trailing behind until the gravitational pull of its big sister drew it in.
The researchers call the low-velocity collision the "big splat" and say it left the single, bulked-up, but ever-so-slightly lopsided moon we now see. It all would have happened long before there was any life on Earth to witness the sight and could explain why the moon's far side is so much more hilly than the one that is always facing Earth.
The researchers back up the theory with computer model runs and an illustration showing how it might have happened.
Outside experts say the idea makes sense but stop short of saying they're convinced.
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