Uses of linear polarization as a probe of extrasolar planet atmospheres

We point out some advantages of making observations of extrasolar planets in linearly polarized (LP) light. Older cool stars have quite low levels (similar to 10(-4) to 10(-5)) of fractional LP, while extrasolar planets can have relatively high fractional LP (similar to 0.1). Observations in LP light can therefore significantly enhance contrast between the planet and its parent star. Data on LP as a function of planetary orbital phase can be used to diagnose the properties (e.g., composition, size, and shape) of the scatterers in the planetary atmosphere. We discuss the feasibility of LP observations of extrasolar planets.