New studies based on the results so far from the Kepler mission estimate that there are billions of other worlds out there, in our galaxy alone. The latest, from scientists at NASA’s Jet Propulsion Laboratory, indicates that 1.4 to 2.7 percent, or one out of every 37 to 70, of sun-like stars are expected to have planets similar in size to the Earth that orbit within the habitable zone of those stars, where temperatures could allow liquid water. That’s about 2 billion in just our galaxy. Also of note is that red dwarf stars can also have such planets, although harder to detect, and those stars are much more numerous than sun-like stars. The full paper (PDF) is here.
A previous recent estimate from Kepler scientists also puts the number of total planets in our galaxy, of various types, at 50 billion, and likely more than that according to Kepler science chief William Borucki. Then there are the at least 50 billion known galaxies.
It seems Carl Sagan knew what he was talking about when he used to say his famous phrase of “billions and billions”… how right he was.