A NASA satellite launched in 2009 March to search for extrasolar planets. It monitors a field of 100 000 main-sequence stars in Cygnus for four years or more with a 0.95-m Schmidt telescope, looking for dips in their light caused by the transit of planets. Kepler will be able to detect planets as small as Mercury. The spacecraft was launched into an Earth-trailing heliocentric orbit with a period of 372.5 days, in which the spacecraft slowly drifts away from Earth.
http://kepler.nasa.gov/ Official mission website.