Kepler, a NASA Discovery mission, is a spaceborne telescope designed to look for Earth-like planets around stars beyond our solar system.
"The Kepler Mission will, for the first time, enable humans to search our galaxy for Earth-size or even smaller planets," said principal investigator William Borucki of NASA's Ames research Center, Moffett Field,
California. "With this cutting-edge capability, Kepler may help us answer one of the most enduring questions humans have asked throughout history: Are there others like us in the universe?"
Kepler will detect planets indirectly, using the "transit" method. A transit occurs each time a planet crosses the line-of-sight between the planet's parent star that it is orbiting and the observer. When this happens, the planet blocks some of the light from its star, resulting in a periodic dimming. This periodic signature is used to detect the planet and to determine its size and its orbit.
Three transits of a star, all with a consistent period, brightness change and duration, provide a robust method of detection and planet confirmation. The measured orbit of the planet and the known properties of the parent star are used to determine if each planet discovered is in the habitable zone; that is, at the distance from its star where liquid water could exist on the surface of the planet.
The industrial partner for development of the hardware is Ball Aerospace & Technologies Corp., based in Boulder, Colorado. The mission is managed by NASA's Jet Propulsion Laboratory.
Scheduled to launch in 2007, Kepler will hunt for planets using a specialized one-meter diameter telescope called a photometer to measure the small changes in brightness caused by the transits.
The key technology at the heart of the photometer is a set of charged coupled devices (CCDs) that measures the brightness of hundreds of thousands of stars at the same time. CCDs are the silicon light-sensitive chips that are used in today's TV cameras, camcorders and digital cameras. Kepler must monitor many thousands of stars simultaneously, since the chance of any one planet being aligned along the line-of-sight is only about 1/2 of a percent.
Over a four-year period, Kepler will continuously view an amount of sky about equal to the size of a human hand held at arm's length or about equal in area to two "scoops" of the sky made with the Big Dipper constellation. In comparison, the Hubble Space Telescope can view only the amount of sky equal to a grain of sand held at arms length, and then only for about a half-hour at a time.
NASA selected Kepler as one of two Discovery missions from 26 proposals made in early 2001. The missions must stay within the Discovery Program's development cost cap of about $299 million. The Discovery Program emphasizes lower-cost, highly focused scientific missions.