... Prowling for Planets . ... Even though we had good reason to believe planets orbit other stars like the Sun, just five years did we uncover the first evidence to support this belief. ... Long ago, astronomers reasoned that the presence of extrasolar planets could be inferred by the gravitational tug they exert on the star: as a planet orbits a star, it drags the star around a common center of gravity. ... Here is an artist's conception of an extrasolar planet passing in front of its parent star. ...