Astronomers have found dozens of potentially habitable planets outside of our solar system. That's dozens of chances to discover the first alien life! Or plenty of places we could park our first interstellar colonies!
But with so many options, how do we know which is best? You might think the most Earth-like planets should be top of our list. After all, we've got water, land, an atmosphere, and trillions of life forms lapping it all up.
