Flying saucers and alien abductions aside, there’s no evidence that Earth has been visited by life from other worlds. In fact, we haven’t found any evidence of intelligent life anywhere else in the universe.
To Enrico Fermi, that lack of neighbors was puzzling. Decades ago, the physicist considered the likely number of planets, the age of the universe, and other factors. And he calculated that everywhere we look, aliens ought to be looking back.
That could mean that we’re alone, or that we’re just not looking hard enough. And according to one present-day scientist, it could also mean that many of the aliens don’t know the rest of the universe exists.
Alan Stern heads New Horizons, a mission that flew past Pluto a couple of years ago. The craft found that an ocean of liquid water could lie below Pluto’s crust. Similar oceans probably exist on several moons of the giant outer planets, and perhaps on other solar-system worlds as well. That makes them much more common than worlds with water on the surface — Earth is the only one.
If such worlds are as common in other star systems, Stern says they could be common homes for life as well. With a solid crust above it, such life might not know that its home world has a “surface,” or that there are other worlds beyond. Such a civilization would be trapped, unable to explore or communicate with the rest of the universe — limiting the number of aliens in our own cosmic neighborhood.
Script by Damond Benningfield