NASA Kepler Space Telescope

You’d be hard-pressed to get a NASA scientist to come out and say that the Kepler space telescope is designed to find aliens. Put it this way, though: The goal of the probe, which was launched in March, is to find planets much like our own in distant star systems—Earth-size bodies orbiting their stars in the sweet spot where the temperature is appropriate to support, just maybe, alien life. Using a photometer that’s more than three feet in diameter, Kepler is now continuously observing some 100,000 stars located between 600 and 3,000 light-years away. It’s looking for the faint dimming of a star that occurs when an orbiting planet passes in front of it. Observe three such blips on a strictly periodic schedule over the course of three years, and you have a planet with a one-year orbit. If the star is approximately the same size as our sun, it could be the center of a planetary system much like our own—and that planet could be habitable. Scientists hope that Kepler could find dozens of habitable planets during its three-to-four-year mission.
kepler.nasa.gov