PH1

PH1b (standing for "Planet Hunters 1"), or by its NASA designation Kepler-64b, is an extrasolar planet found in a circumbinary orbit in the quadruple star system Kepler-64. The planet was discovered by two amateur astronomers from the Planet Hunters project of amateur astronomers using data from the Kepler space telescope with assistance of a Yale University team of international astronomers. The discovery was announced on 15 October 2012. It is the first known transiting planet in a quadruple star system, first known circumbinary planet in a quadruple star system, and the first planet in a quadruple star system found. It was the first confirmed planet discovered by PlanetHunters.org. An independent and nearly simultaneous detection was also reported from a revision of Kepler space telescope data using a transit detection algorithm.

==Star system== The giant planet is Neptune-sized, about 20-55 Earth-masses (). It has a radius 6.2 times that of Earth. The star system is 7200 light years from Earth. The planet orbits a close binary, with a more distant binary orbiting at a distance, forming the quadruple star system. The star system has the Kepler Input Catalogue name KIC 4862625 as well as the designation Kepler-64. The close binary (Aa+Ab) that the planet circles has an orbital period of 20 days. They form an eclipsing binary pair. The two stars are (Aa) 1.384 solar mass () F-type main-sequence star and (Ab) red dwarf. The planet orbits this binary pair in a 138.3-day orbit. The binary pairs have a separation of 1000 AU. A photometric-dynamical model was used to model the planetary system of the close binary pair. The distant binary (Ba+Bb) have a pair separation of 60 AU. The two stars are (Ba) G-type main-sequence star and (Bb) red dwarf. The quadruple star system has an estimated age of two billion years (2 gigayears). The system is located at right ascension declination , so also has a 2MASS catalogue entry of 2MASS 19525162+3957183