The mission will spend three and a half years surveying more than 100,000 sun-like stars in the Cygnus-Lyra region of our Milky Way galaxy. It is expected to find hundreds of planets the size of Earth and larger at various distances from their stars. If Earth-size planets are common in the habitable zone, Kepler could find dozens; if those planets are rare, Kepler might find none. In the end, the mission will be our first step toward answering a question posed by the ancient Greeks: are there other worlds like ours or are we alone?
The Kepler telescope is specially designed to detect the periodic dimming of stars that planets cause as they pass by. Some star systems are oriented in such a way that their planets cross in front of their stars, as seen from our Earthly point of view. As the planets pass by, they cause their stars' light to slightly dim, or wink. The telescope can detect even the faintest of these winks, registering changes in brightness of only 20 parts per million. To achieve this resolution, Kepler will use the largest camera ever launched into space, a 95-megapixel array of charged couple devices, known as CCDs. By staring at one large patch of sky for the duration of its lifetime, Kepler will be able to watch planets periodically transit their stars over multiple cycles. This will allow astronomers to confirm the presence of planets. Earth-size planets in habitable zones would theoretically take about a year to complete one orbit, so Kepler will monitor those stars for at least three years to confirm their presence. Ground-based telescopes and NASA's Hubble and Spitzer space telescopes will perform follow-up studies on the larger planets. Kepler is a NASA Discovery mission. Ames is the home organization of the science principal investigator, and is responsible for the ground system development, mission operations and science data analysis. JPL manages the Kepler mission development. Ball Aerospace & Technologies Corp. of Boulder, Colorado, is responsible for developing the Kepler flight system and supporting mission operations.
(Source: NASA Kepler — The photo shows the Kepler spacecraft being moved inside a protective container out of the Astrotech facility in Titusville, Fla., to begin its trek to Launch Complex 17 at the Cape Canaveral Air Force Station. There, it will be hoisted atop the Delta II rocket that is to send it into space. Image credit: NASA/Jack Pfaller)