Detection of Other Planetary Systems Using Photometry

Abstract

Detection of extrasolar short-period planets, particularly if they are in the liquid-water zone, would be one of the most exciting discoveries of our lifetime. A well-planned space mission has the capability of making this discovery using the photometric method. An Earth-sized planet transiting a Sun-like star will cause a decrease in the apparent luminosity of the star by one part in 10,000 with a duration of about 12 hours and a period of about one year. Given a random orientation of orbital plane alignments with the line-of-sight to a star, and assuming our solar system to be typical, one would expect 1 percent of the stars monitored to exhibit planetary transits. A null result would also be significant and indicate that Earth-sized planets are rare. For the mission to be successful one needs a sensor system that can simultaneously monitor many thousands of stars with a photometric precision of one part in 30,000 per hour of integration. Confirmation of a detection will involve detection of a second transit that will yield a period and predict the time for a third and subsequent transits. The technology issues that need to be addressed are twofold: one is for an appropriate optical design; the other is for a detector system with the necessary photometric precision. Two candidates for the detector system are silicon diodes and CCD's.