A news piece from the Niels Bohr Institute, University of Copenhagen:
Astronomers have discovered thousands of exoplanets in our galaxy, the Milky Way, using the Kepler satellite and many of them have multiple planets orbiting the host star. By analysing these planetary systems, researchers from the Australian National University and the Niels Bohr Institute in Copenhagen have calculated the probability for the number of stars in the Milky Way that might have planets in the habitable zone. The calculations show that billions of the stars in the Milky Way will have one to three planets in the habitable zone, where there is the potential for liquid water and where life could exist.
I like those numbers. Of course it doesn’t get us any closer to the alien swimmers (or swingers, or gliders) themselves. But if there’s a chance we’re not alone, it’s good to know how remote the odds are.