When NASA talks about “Earth-like” planets, it’s referring to ones that are about the same size as Earth, and that orbit stars in a warm, habitable zone where liquid water could exist on their surface. In order to detect such planets, the Kepler has been using its 96 million pixel camera to measure fluctuations in the brightness of the Cygnus-Lyra stars. The degree to which a star dims when an object moves in front of it can be used to determine its proximity to the orbiting body. The disturbance in brightness caused by the orbit of an Earth-like planet would be roughly 1 part per 10,000. From the data received so far, the 28-member Kepler team are taking a closer look at over 400 “objects of interest.” They are doing so through the use of ground-based telescopes, the Hubble Space Telescope, and the Spitzer Space Telescope. Such follow-up work is necessary to weed out false alarms, such as binary stars that orbit one another. Ground-based stereoscopic telescopes are also necessary for determining the size of the stars, which would in turn indicate the size of the planets passing in front of them.

(Source: NASA/JPL-Caltech)