Direct Spectroscopic Detection of Extrasolar Planets

(Jones, Barnes, Pinfield)

Direct imaging techniques will have great difficulty detecting such planets, because the planet is so much fainter than the star and because their two images are never separated on the sky by more than 0.003 seconds of arc. Fortunately, however, the starlight scattered from the planet can be distinguished from the direct starlight because the scattered light is Doppler shifted by virtue of the close-in planet's relatively fast orbital velocity (~ 150 km/sec). Superimposed on the pattern given by the planet's albedo changing slowly with wavelength, the spectrum of the planet's light will retain the same pattern of photospheric absorption lines as in the direct starlight.