In the class, we learn about the astrometric technique, Doppler technique and direct imaging used to detect extrasolar planets. And in this blog, I’d like to introduce some other planet-hunting strategies that have proved to be applicable. The first method is called gravitational microlensing. A gravitational microlensing occurs only when two stars are almost exactly aligned and lasts for several days, during which time the gravitational field of a star will act like a lens to magnify the light of a background distant star. And if the foreground star has an orbiting planet, the contribution of the planet’s gravitational field to the lensing effect can also be detected. Since the center of our galaxy can provide huge amounts of background stars, the method is most useful for detecting planets between Earth and galactic center. The second method is called polarimetry. The light given off by a star is unpolarized, but when the light is reflected off the atmosphere of a planet, it will become polarized. Since polarimetry is not limited by the stability of Earth’s atmosphere, such measurements can be made with very high sensitivity and allow scientists to determine the composition of extrasolar planet’s atmosphere. However, planets with no atmosphere can never be detected by such method.