First planetary system with two suns discovered
This artist's concept illustrates Kepler-47, the first transiting circumbinary system -- multiple planets orbiting two suns – 4,900 light-years from Earth, in the constellation Cygnus. (Photo/NASA)
NASA's Kepler mission has found the first multi-planet system orbiting two suns for the first time.
Located roughly 5,000 light-years away in the constellation Cygnus, the system is known as Kepler-47. Astronomers detected two planets in the Kepler-47 system, a pair of orbiting stars that eclipse each other every 7.5 days from our vantage point on Earth. One star is similar to the sun in size, but only 84 percent as bright. The second star is diminutive, measuring only one-third the size of the sun and less than 1 percent as bright.
Launched in March 2009, Kepler was designed to discover Earth- size planets orbiting other stars. Kepler searches for distant worlds by looking for "transits," when a planet passes in front of a star, briefly causing it to dim. The amount of dimming reveals the size of the planet compared to the size of the star.
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（Editor：陈丽丹、张茜）
