When Will We Find Another Earth?

The biggest growth industry in astronomy right now is finding exoplanets; alien worlds orbiting alien stars. This was essentially impossible even 25 years ago, but now better technology and techniques mean a new one is announced several times a week! Usually, these planets are big, more like Jupiter than our own home world. As we get better at searching, though, we're finding smaller and more familiar planets. Slate is kicking off a month of articles about Big Questions, and certainly one of the...