Earth May Once Have Had Two Moons That Collided to Form the One We Know
Epic Collision A slow-motion collision between Earth's moon and a smaller companion would have destroyed the smaller celestial body and scattered its remains across the far side of our surviving satellite. Martin Jutzi/Erik Asphaug/Nature A primordial second moon may have smacked into our existing moon billions of years ago, its remains pancaking across its larger sibling and disrupting the bigger moon's still-cooling surface. This new theory could explain why the moon's far side looks so different from the one that perennially faces us. Both moons would have coalesced from the remnants of debris ejected when a Mars-sized object whacked the Earth early in its formation, scientists say. Most moon-formation theories have suggested our sole satellite formed from that chaotic jumble. But a new paper published today in Nature says a tiny Trojan moon, about one-thirtieth the size of the one we have today, survived as well, inhabiting a Lagrange point 60 degrees...