What goes up, come down. If it's a satellite or a spaceship then you hope it comes down in the South Pacific in a place as far away from inhabited land as possible. Someday someone (some alien?) is going to across all the space junk currently sitting at the bottom of the sea—only by then it will be embedded in a rock atop a mountain—and wonder what the heck happened here. It's a PhD thesis in the making. Fascinating read via How Stuff Works.