WASHINGTON - Earth once had two moons, astronomers suggested Wednesday. But in a spectacle that might have beguiled poets, lovers, and songwriters if only they had been around to see it billions of years ago, the smaller one smashed into the other in a "big splat."
The result: a single bulked-up and ever-so-slightly lopsided moon.
The astronomers came up with the scenario to explain why the moon's far side is so much hillier than the one that is always facing Earth.
The theory, outlined in the journal Nature, comes complete with computer-model runs showing how it might have happened, 4.4 billion years ago, as a small moon that trailed behind a much larger one got pulled in by gravity at 5,000 m.p.h.