ON THE FEASIBILITY OF DETECTING EXTRASOLAR PLANETS BY REFLECTED STARLIGHT USING THE HUBBLE SPACE TELESCOPE

Detecting extrasolar planets in reflected stellar radiation is an exceedingly challenging task due to the great faintness of planets as compared with stars. When a telescope focuses two close sources on a detector, the fainter source can be "discovered" only if the signal recorded near the location of its image is convincingly larger than would be expected or observed in its absence. We investigate the implications of this criterion for planet searches using the Hubble Space Telescope (HST). Using the best available metrology data, we estimate the HST point-spread function (PSF) in both the center and the wing. We define the maximum star-planet flux ratio. We introduce a figure of merit, Q, which is the contrast ratio between a best-case planet and the background of scattered star light. For HST, the value of Q is unfavorable for detecting planets. © 1990.