<P> An exoplanet (UK: / ˈɛk. soʊˌplæn. ɪt /, US: / ˌɛk. soʊˈplæn. ɪt /) or extrasolar planet is a planet outside our 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 was in 1988, although it was not accepted as an exoplanet until later . The first confirmed detection occurred in 1992 . As of 1 August 2018, there are 3,815 confirmed planets in 2,853 systems, with 633 systems having more than one planet . </P> <P> The High Accuracy Radial Velocity Planet Searcher (HARPS), since 2004) has discovered about a hundred exoplanets while the Kepler space telescope (since 2009) has found more than two thousand . Kepler has also detected a few thousand candidate planets, of which about 11% may be false positives . In several cases, multiple planets have been observed around a star . About 1 in 5 Sun - like stars have an "Earth - sized" planet in the habitable zone . Assuming there are 200 billion stars in the Milky Way, one can hypothesize that there are 11 billion potentially habitable Earth - sized planets in the Milky Way, rising to 40 billion if planets orbiting the numerous red dwarfs are included . </P>

When was first planet outside solar system discovered
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