The Kepler Mission: Finding the Sizes, Orbits and Frequencies of Earth-size and Larger Extrasolar Planets

The first step in discovering the extent of life in our galaxy is to determine the number of terrestrial planets in circumstellar habitable zones (HZ). The Kepler Mission is designed around a 0.95 m aperture Schmidt-type telescope with an array of 42 CCDs. The photometer is designed to continuously monitor the brightness of 100,000 solar-like stars to detect the transits of Earth-size and larger planets. It is scheduled to be launched into a heliocentric orbit in 2007. Measurements of the depth and repetition time of transits provide the size of the planet relative to the star and its orbital period. When combined with ground-based spectroscopy of these stars to fix the stellar parameters, the true planet radius and orbit, semi-major axis, hence the position relative to the HZ, are determined. The spectra are also used to discover the relationships between the characteristics of planets and the stars that they orbit. In particular, the association of planetary size and occurrence frequency with stellar mass and metallicity will be investigated. At the end of the four year mission, hundreds of terrestrial planets should be discovered in and near the HZ of their stars if such planets are common. Extending the mission to six years doubles the expected number of Earth-size planets in the HZ. A null result would imply that terrestrial planets in the HZ occur in less than 1% of the stars and that habitable planets might be quite rare. Based on the results of the current Doppler velocity discoveries, detection of the reflected light from several hundred short-period giant planets is also expected. Information on the albedos and densities of those giants showing transits will be obtained.