<P> An exoplanet (extrasolar planet) is a planet located outside the Solar System . The first evidence of an exoplanet was noted as early as 1917, but was not recognized as such . However, the first scientific detection of an exoplanet began in 1988 . Shortly afterwards, the first confirmed detection came in 1992, with the discovery of several terrestrial - mass planets orbiting the pulsar PSR B1257 + 12 . The first confirmation of an exoplanet orbiting a main - sequence star was made in 1995, when a giant planet was found in a four - day orbit around the nearby star 51 Pegasi . Some exoplanets have been imaged directly by telescopes, but the vast majority have been detected through indirect methods, such as the transit method and the radial - velocity method . As of 1 December 2017, there are 3,710 planets in 2,780 systems, with 621 systems having more than one planet . This is a list of the most notable discoveries: </P> <Ul> <Li> Gamma Cephei Ab: The radial velocity variations of the star Gamma Cephei were announced in 1989, consistent with a planet in a 2.5 - year orbit . However, misclassification of the star as a giant combined with an underestimation of the orbit of the Gamma Cephei binary, which implied the planet's orbit would be unstable, led some astronomers to suspect the variations were merely due to stellar rotation . The existence of the planet was finally confirmed in 2002 . </Li> <Li> HD 114762 b: This object has a minimum mass 11 times the mass of Jupiter and has an 89 - day orbit . At the time of its discovery it was regarded as a probable brown dwarf, although subsequently it has been included in catalogues of extrasolar planets . </Li> <Li> PSR B1257 + 12: The first confirmed discovery of extrasolar planets was made in 1992 when a system of terrestrial - mass planets was announced to be present around the millisecond pulsar PSR B1257 + 12 . </Li> </Ul> <Li> Gamma Cephei Ab: The radial velocity variations of the star Gamma Cephei were announced in 1989, consistent with a planet in a 2.5 - year orbit . However, misclassification of the star as a giant combined with an underestimation of the orbit of the Gamma Cephei binary, which implied the planet's orbit would be unstable, led some astronomers to suspect the variations were merely due to stellar rotation . The existence of the planet was finally confirmed in 2002 . </Li> <Li> HD 114762 b: This object has a minimum mass 11 times the mass of Jupiter and has an 89 - day orbit . At the time of its discovery it was regarded as a probable brown dwarf, although subsequently it has been included in catalogues of extrasolar planets . </Li>

The first series of extrasolar planets that were discovered were found by which method