Probing the atmospheres of planets orbiting microlensed stars via polarization variability

We present a new method to identify and probe planetary companions of stars in the Galactic bulge and Magellanic Clouds using gravitational microlensi ng. While spectroscopic study of these planets is well beyond current obser vational techniques, monitoring polarization fluctuations during high-magni fication events induced by binary microlensing events will probe the compos ition of the planetary atmospheres, an observation which otherwise is curre ntly unattainable even for nearby planetary systems.