How do we find planets — even habitable planets — around other stars? By looking for tiny dimming as a planet passes in front of its sun, TED Fellow Lucianne Walkowicz and the Kepler mission have found some 1,200 potential new planetary systems. With new techniques, they may even find ones with the right conditions for life.
A prior method of detecting planets around other stars was looking for the wobble. As planets orbit their star, they affect the position of the star. The more mass the planet has, the more the wobble and easier to detect. Of course, a shorter orbit also makes it easier to detect. So it was really good at locating gas giants like Jupiter or larger as close as Mercury or Venus. It would not find an Earth.
Kepler has done a fantastic job so far locating planets, especially those near the size of Earth. Apparently we can even participate by looking for the light dips through the Planet Hunters web site. (Kind of surprised this is not automated. But then, getting credit for having helped find a star is pretty cool.)
If you cannot see the video below, visit Finding planets around other stars.