Counting Exoplanets

Astronomers have now found roughly 500 planets orbiting other stars. The number is not exact because there's a possibility some of those may turn out to be false positives, but astronomers are confident the vast majority of the finds will hold up.

This first 500, of course, is literally only the beginning. Kepler, NASA's planet-hunting spacecraft, has already identified 700 stars that might have at least one planet, and its mission has barely begun; Kepler will almost certainly find hundreds or thousands more stars over the next few years. Other searches, using various strategies, will no doubt find even more.

Astronomers, however, are more intrigued by the variety of worlds they've found than by the sheer number. They are getting closer and closer to being able to identify worlds similar to Earth, and along the way they have found huge planets in orbits they never would have imagined, planets orbiting in the habitable zone of their stars, and even one that seems to have stayed with its star as the Milky Way absorbed its original home galaxy.