Milky Way Has 500 Million Theoretically Habitable Planets
NASA estimated the number of planets by extrapolating from a sample that they found during a year of searching with the Kepler telescope. (Here's a fun little '80s-style animation that shows you how the telescope finds planets, by the way.) Their estimate was based on the assumption that one out of two stars has planets, and the Milky Way has at least 100 billion stars.
Anyway -- when do we make contact with the aliens?