Planet Espresso

A long time ago -- 4.56 billion years ago, give or take an eon or two -- the Earth upon which you currently live wasn't here. Well, not all in one place, at least: It was actually scattered over trillions of cubic kilometers of space, occupying part of a dust-laden disk orbiting the just-forming Sun. This disk was huge, hundreds of thousands of kilometers thick, and stretching for billions of kilometers out from the Sun. But it wouldn't stay that way: Over time, pieces of it stuck together, get...