Number of potentially habitable planets in our galaxy: Tens of billions

It is one thing to observe the periodic dimming of a star’s light, as NASA’s Kepler Space Telescope has done for thousands of planet “candidates” since its launch in 2009. However, to confirm that such dimmings are in fact due to a planet passing in front of a star, as opposed to any number of false positives such as a binary star companion, requires intensive follow-up work with ground-based instruments, most often a measurement of radial velocity to determine the object’s mass.

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Story added 11. May 2016, content source with full text you can find at link above.