Extra-solar planets are very difficult to see because they are outshone by the light from their parent stars. It can be deter-mined whether or not a star has a planetary system by observing whether or not the star’s- light “wobbles”. As a planet orbits a star, its gravitational pull will cause the star’s light to bend slightly, and thus to change colour. This technique only works for giant planets, however, because an Earth-sized world would have little effect on its parent.
It is not easy to detect another planet so far away from Earth. Unlike stars which are fueled by nuclear reactions, planets only reflect the optical light of their stellar companion. In our solar system, for example, the Sun outshines its planets about one billion times in visible light. Because of the distant planets’ faintness near the brightness of the nearby star, astronomers have had to devise clever methods to detect them. Currently, the most successful approach is based on the fact that a nearby planet will cause the star to wobble back and forth just a bit as the planet revolves around it. Astronomers can detect this tiny wobble and then calculate the orbit and mass of the object which is causing it. Even using this technique, however, it is still not easy to detect planets around other stars. Consider this: someone looking at our Sun from 30 light-years away would see it wobbling in a circle whose size would be about as big as a quarter viewed from 10,000 kilometers away!
During the past few years, researchers have detected over a dozen planets orbiting sunlike stars. The first was reported in October 1995 by Michel Mayor and Didier Queloz of the Geneva Observatory in Switzerland. While observing the star 51 Pegasi, they noticed a change in the light from the star – its light repeatedly shifted back and forth between the blue and red ends of the electromagnetic spectrum. The timing of this Doppler shift implied that the star was “wobbling” a little because of a closely orbiting planet. In fact, the planet appeared to be revolving around the star every 4.2 days. Shortly thereafter, a survey of over a hundred other sunlike stars performed by the team of Geoff Marcy and Paul Butler at San Francisco State University and the University of California at Berkeley, turned up six more such planets. Of those, one planet circling the star 16 Cygni B was independently discovered by astronomers William D. Cochran and Artie P. Hatzes of the University of Texas McDonald Observatory. Since 1996, the announcement of the detection of new planets has become fairly routine….but always exciting!