{FD} Does humanity really need a backup Earth?

SpaceX CEO Elon Musk has a vision: He wants to get humans to Mars as soon as possible. He already wowed the world this year, when the Falcon Heavy launched and flung a Tesla car toward the asteroid belt. And this heavy-lift rocket will be dwarfed by the boosters Musk plans for Mars exploration, which he says will carry colonists in fleets of ships to the Red Planet.