Every one of us has wondered if we're alone in the universe. Are there living things elsewhere? Is the Earth the only place we'll ever know that has life? That's the question posed by this month's cover story in National Geographic. It's one I think we can answer, and maybe sooner than you think.

Many of us think of alien life the way it's depicted in science fiction—creatures that look quite a bit like humans in makeup and that all speak English with a non-American accent. These made-up aliens hail from distant star systems. But there's a place right here in our own solar system that may be teeming with life. It's Europa, a moon of Jupiter, one of the