There could be as many as 400 billion stars in the Milky Way. Even if we suppose only a quarter of those stars have planets, and if only a quarter of those planetary systems contain conditions suitable for the development of life, then there could still be hundreds of millions of places in our galaxy that are teeming with organisms. We've yet to discover life outside of our planet, but here's our list of the seven most likely locales. (Text: Bryan Nelson)