Extrasolar planets or exoplanets are planets which are found outside our own solar system. Study of the universe has revealed over 200 of these planetary bodies, and many more will probably continue to be found as human study of astronomy becomes even more sophisticated. Several universities and observatories have exoplanet research facilities which are dedicated to seeking out and identifying these planets, which is no mean feat when they are billions of light years away.
The presence of exoplanets was hypothesized by numerous scientists and astronomers for centuries before the existence of an exoplanet was finally confirmed in 1988. A group of Canadian astronomers managed to identify a mass which they believed was an exoplanet; after much debate over this initial discovery, their discovery was confirmed independently in 2003. Since 1988, a number of exoplanets have been discovered, primarily gas planets like Jupiter.
Researchers who work on exoplanets theorize that planets which are similar to Earth may be discovered at some point. Several likely candidates have been identified, providing hope that life forms may have arisen in other parts of the universe. The existence of more gas giants such as Jupiter is also promising, as some researchers believe that Jupiter helped to shield the Earth during the formation of the solar system, allowing it to become a planet which could sustain life. This function may be served by gas giants in other solar systems as well.
Locating an exoplanet is rather challenging, as the masses do not emit as much light as stars, making them difficult to find through telescope observation. Many advanced astronomical imaging techniques are used in the pursuit of exoplanets. Some researchers look for exoplanets by looking for characteristic changes in stars and other astrological phenomena, as planets leave distinctive signatures even if they cannot be seen. Occasionally, an exoplanet is found during transit, when it passes in front of its parent star, briefly dimming the star's light.
Unlike the planets in our solar system, exoplanets do not have terribly creative names. They are named after the stars that they orbit in the order of discovery, using a small lower case letter to denote each exoplanet, as in the case of gamma Cep b, a relatively nearby exoplanet. It should be stressed that exoplanets are not named in the order of proximity to the parent star; they are named in order of identification by astronomers. The exact properties of many exoplanets are unknown, since it is difficult to observe details such as signs of life at such a great distance. Scientists hope to some day visit these planets for themselves.