Probable Detection of Starlight Reflected from the Giant Exoplanet Orbiting Τ Boötis

Giant planets orbiting stars other than the Sun are clearly detectable through precise radial-velocity measurements of the orbital reflex motion of the parent star. In the four years since the discovery 1 of the companion to the star 51 Peg, similar low-amplitude " Doppler star wobbles " have revealed the presence of some 20 planets orbiting nearby solar-type stars. Several of these newly-discovered planets 2, 3, 4 are very close to their parent stars, in orbits with periods of only a few days. Being an indirect technique, however, the reflex-velocity method has little to say about the sizes or compositions of the planets, and can only place lower limits on their masses. Here we report the use of high-resolution optical spectroscopy to achieve a probable detection of the 1