|Green area = habitable zone. Credit: NASA-JPL-Caltech|
How Does the Kepler Satellite Work?
The Kepler Satellite monitors the brightness of more than 100,000 stars for the life of the mission, which is expected to be extended beyond its current 3.5 years. The satellite was launched in March 2009. It observes the changes in brightness of these stars when planets pass in front of them. The size of a transiting planet is found from the size of its star and 'the deepness of the transit', which is the decrease in brightness of a star when a planet passes in front of it. Since Earth-like planets create 'small' dips in brightness, i.e., close to the noise level of the instrument, the Kepler mission requires three transits to declare a detection. This, of course, takes time and it is why we have to wait before even smaller Earth-like planets will be reported.