The Kepler spacecraft, launched by NASA in March to look for cousins of Earth—those planets around other stars that have the right conditions for life—is now on the job. The spacecraft is in position, trailing Earth in an orbit around the sun, and has completed a tune-up of its instruments.

"Now the fun begins," Kepler principal investigator Bill Borucki of the NASA Ames Research Center in Moffett Field, Calif., said in a statement. "We are all really excited to start sorting through the data and discovering the planets."

Over the next three-plus years, Kepler will train its cameralike eye on a patch of 100,000 stars, carefully monitoring their brightness over time. Where there are planets in orbit across Kepler's line of sight, a periodic dip in the star's glow will give them away.

While a planet similar to Earth—that is, a planet in a roughly yearlong orbit—will likely take the bulk of Kepler's mission to conclusively identify, NASA says that larger gas giants in tighter orbits, the so-called hot Jupiters, could be announced as early as next year. Such hot, massive planets have already been found in relatively large numbers, but Kepler will likely be the first to discover a truly habitable world—not too hot, not too cold—outside the solar system.

Artist's conception of Kepler, along with a map of its field of view: NASA/JPL