ABSTRACT.A small CCD photometer dedicated to the detection of extrasolar planets has been developed and put into operation at Mount Hamilton, California. It simultaneously monitors 6000 stars brighter than 13th magnitude in its 49 deg 2 field of view. Observations are conducted all night every clear night of the year. A single field is monitored at a cadence of eight images per hour for a period of about 3 months. When the data are folded for the purpose of discovering low-amplitude transits, transit amplitudes of 1% are readily detected. This precision is sufficient to find Jovian-size planets orbiting solar-like stars, which have signal amplitudes from 1% to 2% depending on the inflation of the planet's atmosphere and the size of the star. An investigation of possible noise sources indicates that neither star field crowding, scintillation noise, nor photon shot noise are the major noise sources for stars brighter than visual magnitude 11.6.Over one hundred variable stars have been found in each star field. About 50 of these stars are eclipsing binary stars, several with transit amplitudes of only a few percent. Three stars that showed only primary transits were examined with high-precision spectroscopy. Two were found to be nearly identical stars in binary pairs orbiting at double the photometric period. Spectroscopic observations showed the third star to be a high mass ratio single-lined binary. On 1999 November 22 the transit of a planet orbiting HD 209458 was observed and the predicted amplitude and immersion times were confirmed. These observations show that the photometer and the data reduction and analysis algorithms have the necessary precision to find companions with the expected area ratio for Jovian-size planets orbiting solar-like stars.

With the detection of giant extrasolar planets and the quest for life on Mars, there is heightened interest in finding earth-class planets, those that are less than ten earth masses and might be life supporting. A space-based photometer has the ability to detect the periodic transits of earth-class planets for a wide variety ofspectral types ofstars. From the data and known type of host star, the orbital semi-major axis, size and characteristic temperature of each planet can be calculated. The frequency of planet formation with respect to spectral type and occurrence for both singular and multiple-stellar systems can be determined.A description is presented of a one-meter aperture photometer with a twelve-degree field of view and a focal plane of 21 CCDs. The photometer would continuously and simultaneously monitor 160,000 stars of visual magnitude 14. Its onesigma system sensitivity for a transit of a twelfth magnitude solar-like star by a planet of one-earth radius would be one part in 50,000. It is anticipated that about 480 earth-class planets (O.5M1O M) would be detected along with 140 giant planets in transit and 1400 giant planets by reflected light. Densities could be derived for about seven cases where the planet is seen in transit and radial velocities are measurable.

The thirty or so extrasolar planets that have been discovered to date are all about as large as Jupiter or larger. Finding Earthsize planets is a substantially more difficult task. We propose the use of spacebased differential photometry to detect the periodic changes in brightness of several hours duration caused by planets transiting their parent stars. The change in brightness for a Sun-Earth analog transit is 8x105. We describe the instrument and mission concepts that will monitor 100,000 main-sequence stars and detect on the order of 500 Earth-size planets, if terrestrial planets are common in the extended solar neighborhood.We have performed and will discuss end-to-end laboratory measurements that demonstrate the feasibility of differential photometry under realistic operating conditions. The tests included a realistic star field in which individual transits can be generated, fast optics with a realistic point spread function, and a flight-type back-illuminated CCD. Spacecraft motion was simulated using piezoelectric transducers. Data acquisition and processing used the same methods as planned for the space mission. A system-level differential-photometric precision of 1 O has been demonstrated under realistic conditions.

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A point design for a mission to detect Earth‐sized planets in the inner orbits of solar‐like stars is described. The observing technique is based upon continuously and simultaneously monitoring 5000 solar‐like stars for brightness changes that would be caused by planets transiting their star. Detection of periodic transits of the same amplitude and duration provides for a robust method of discovery. The instrument would consist of a 1‐m Schmidt telescope with an array of charge‐coupled devices (CCDs) filling the 12° field of view. The instrument would be placed in a halo orbit about the L2 Lagrange point, where its viewing would not be obscured at any time by the Sun, Earth, or Moon.