Nevermind Where. *When* Are the Intelligent Aliens?

Only a few decades back, there were serious scientists who thought that planets might be miraculous. Not miracles like a burning bush or a docile teenager, but highly improbable objects. These researchers figured that the conditions necessary for making small, cold worlds could be rare---perhaps extremely rare. Most stars were believed to live their luminous lives alone, bereft of planetary accompaniment.

Well, those thoughts have been banished. In the last 15 years, hard-working astronomers hav