ABSTRACT
As we have pointed out in Chapter 6, the first confirmed detection of a planetary system was in 1992, with the discovery of few terrestrial-mass planets orbiting the pulsar PSR B1257+12. It was in 1995 that the detection of planetary system of a main-sequence star was first confirmed. Giant planet, 51 Pegasi b, was noted in a 4-day orbit around the nearby G-type star 51 Pegasi. The frequencies of detections of exoplanets have increased since then. In particular, tremendous success came through the advancements in methods of detecting extrasolar planets and dedicated planet finding programs such as the Kepler mission. It has been observed that certain characteristics are common in most known exoplanets, as well as the stars they are orbiting. Most of the stars that host planets are mainsequence stars and similar in spectral class to our own Sun. The majority of the known exoplanets are massive, which does not necessarily mean that Earth-sized exoplanets do not exist. In fact, the detection methods we have developed largely favor for finding massive planets orbiting close to stars. Some of them even orbit more closely than Mercury orbits the Sun. Dissimilar to the nearly circular orbits of the planets in our solar system, most exoplanets reveal largely eccentric orbits [1-5]. Major numbers of the known exoplanets are gaseous and similar to the giant planets in our solar system, whereas some of the smaller exoplanets found exhibit signs of rockier compositions. Until recently, there was no evidence that any planets existed around the 100 billion stars in our galaxy, except for around our Sun. However, over the last few decades, we have detected evidence of over a hundred planets orbiting other stars, even though they are far too small to be observed by any telescope. But we know their presence because of the effect they have on their host star. At the time when a planet orbits a star, its gravity causes the star to wobble. Changes in the wavelength of the light arriving from the star can be detected when the star wobbles in the direction of Earth. This variation of wavelength is known as the Doppler effect and is similar to the variation in pitch of the siren when a police car passes the listener [6-14].
