The first exoplanet was detected in 6 October 1995, and was named 51 Pegasi b.[1] When extrasolar planets are observed to transit their parent stars, astronomers are granted unprecedented access to their physical properties, such as planetary masses and size, which in turn provide fundamental constraints on models of their physical structure.[2] Furthermore, such planets afford the opportunity to study the dynamics and chemistry of their atmospheres.[2]
Statistical surveys and individual characterization are the keys to addressing the fundamental questions in exoplanetology.[3] Through May 2015, varying techniques have been used to discover 1,924 planets outside the Solar System.[4] Documenting the properties of a large sample exoplanets at various ages, orbiting their parent stars of various types, will contribute to increased understanding —or better models— of planetary formation (accretion), geological evolution, orbit migration,[3][5] and their potential habitability.[6]
About 97% of all the known exoplanets, have been discovered by indirect techniques of detection, mainly by radial velocity measurements and transit monitoring techniques.[6] The following methods have proved successful for discovering a new planet or confirming an already discovered planet: [7]
As more planets are discovered, the field of exoplanetology continues to grow into a deeper study of extrasolar worlds, and will ultimately tackle the prospect of life on planets beyond the Solar System.[6] At cosmic distances, life can only be detected if it is developed at a planetary scale and strongly modified the planetary environment, in such a way that the modifications cannot be explained by classical physico-chemical processes (out of equilibrium processes).[6] For example, molecular oxygen (O
2) in the atmosphere of Earth is a result of photosynthesis by living plants and many kinds of microorganisms, so it can be used as a indication of life on exoplanets, although oxygen could also be produced by non-biological means.[8] Furthermore, a potentially habitable planet must orbit a stable star at a distance within which planetary-mass objects with sufficient atmospheric pressure can support liquid water at their surfaces.[9][10]
^ ab"The Era of Comparative Exoplanetology." American Astronomical Society. Charbonneau, David. AAS Meeting #212, #54.01; Bulletin of the American Astronomical Society, May 2008, Vol. 40, p.250
^Ollivier M., Encrenaz T., Roques F., Selsis F., Casoli F., Planetary Systems - Detection, Formation and Habitability of Extrasolar Planets, Springer, Berlin (2008)
