Ever since humans acknowledged the enormity of the universe, we have intuited that life must exist somewhere, either in our galaxy or some galaxy far, far away. If the universe contains billions of galaxies, and if each galaxy contains billions of stars, and if a fraction of those stars have Earth-like planets, then hundreds — maybe even thousands — of aliencivilizations must exist across the cosmos. Right?
Milky Way Image Gallery
For a while, science contented itself with the logic alone. Then, in 1995, astronomers located the first planets outside our solar system. Since then, they’ve detected nearly 300 of these extra-solar planets. Although most are large, hot planets similar to Jupiter(which is why they’re easier to find), smaller, Earth-like planets are beginning to reveal themselves. In June 2008, European astronomers found three planets, all a little larger than Earth, orbiting a star 42 light-years away [source: Vastag].