Astrobiology Workshop, Macquarie University July 12-13 2001

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Detecting Extrasolar Planets by Polarization

Jeremy Bailey (Anglo-Australian Observatory), Phil Lucas and Jim Hough (University of Hertfordshire)

Despite the detection of more than 60 extrasolar planets through their effect on the radial velocity of the stars they orbit, no extrasolar planet has yet been seen directly by its emitted or reflected light. Detections by spectroscopic techniques have so far been unsuccessful while photometric detection requires accuracies which are beyond that which can currently be achieved. We suggest that planets orbiting close to their star (hot Jupiters) could be detected by the polarization of the light scattered from their atmospheres. While the resulting polarization in the combined light of the planet and star is small (10^-5 to 10^-6), polarization measurments can in principle be made with very high sensitivity since polarimetry is a differential measurement and is not limited by the stability of the earth's atmosphere as photometry is. We have designed a stellar polarimeter which should be capable of achieving the required sensitivity. With such an instrument on a 4m or larger telescope we should be able to detect the polarization signature from the planets of bright hot Jupiter systems such as Tau Boo, Upsilon And or 51 Peg.