This giant planet is about half the size of Jupiter and orbits its star in about four days.
This year we celebrate the discovery of 51 Pegasi b in October, 1995. This giant planet is about half the size of Jupiter and orbits its star in about four days. '51 Peg' helped launch a whole new field of exploration. Image credit: NASA/JPL-Caltech
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October 6 marks the 20th anniversary of the first discovery of a planet orbiting a sun-like, or "normal," star beyond our solar system. The planet, called 51 Pegasi b, belongs to a class of planets now known as exoplanets. Since that momentous discovery, thousands more exoplanets have been found in our galaxy.

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As of today, there are more than 1,800 confirmed exoplanets. More than 1,000 of these were discovered by NASA's Kepler mission, breaking wide open the field of exoplanet science. Kepler has even identified some planets with Earth-like traits, such as Kepler-452b, a near-Earth-size planet found in the habitable zone of a sun-like star. The habitable zone is the region around a star where temperatures are just right for one of life's essential ingredients -- water -- to pool on a planet's surface.

NASA's Ames Research Center, Moffett Field, California, manages the Kepler and K2 missions for NASA's Science Mission Directorate. NASA's Jet Propulsion Laboratory in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado Boulder.

For more information about the Kepler mission, visit:

A related feature story about other potentially habitable planets is online at:

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Whitney Clavin
Jet Propulsion Laboratory, Pasadena, California