A Photometric Approach to Detecting Earth-Sized Planets

Abstract

The photometric method of searching for planets around stars depends on observing the decrease in light flux produced by the transit of a planet across the stellar disk. The magnitude of this reduction is proportional to the ratio of the planet’s area to that of the star. For the solar system, the decrease in light amounts to 0.01 per cent for terrestrial-sized planets. To overcome the effects of scintillation and variable extinction in the Earth’s atmosphere, it will be necessary to operate the photometric system on a space platform. The photometric method works only for planets whose orbital plane is near our line of sight. Thus many stars must be monitored to insure that some stars with appropriately-oriented orbital planes are observed. If every solar-type star has a planetary system similar to our solar system, then a photometer that monitors 1000 stars with the requisite precision should detect at least 10 transits per year of observation. Thus a 3-year observation period should allow meaningful statements to be made about the frequency of solar-type planetary systems. A state-of-the-art photometer is being developed to test components and concepts. The goal is the development of a photometer that can routinely measure the relative brightness of stars to a precision of 1 part in 100,000. Such precision should be achievable using “quantum perfect” detectors. Results of field tests of a prototype photometer are promising.