E Pluribus Lunum: Did Earth Once Have Two Moons?

For tens of millions of years--a mere sliver of astronomical time--the night sky above Earth may have been a bit more populous than it is today. For that brief period, our planet may have had not one but two moons, which soon collided and merged into our familiar lunar companion. No one would have been around to see the second moon--the lunar merger would have occurred nearly 4.5 billion years ago, shortly after Earth had formed. [More]

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