The first discovery of two planets orbiting a pair of stars 5,000 light years away was announced Tuesday by a team led by a San Diego State University astronomy professor.
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The system, called Kepler-47, contains two stars in the constellation Cygnus that whirl around each other every 7 1/2 days. One is about as big as the sun while the other is only one-third the size, according to Jerome Orosz of SDSU, the lead author of a study published in Tuesday's edition of the journal Science.
The planets circle around both stars, making them, in scientific terminology, a "transiting circumbinary multi-planet system."
Kepler-47b is three times larger than the diameter of Earth and circles the stars every 49 days. Kepler-47c is a little bigger than Uranus and completes its year in 303 days.
It's the first time planets have been discovered in a chaotic binary star system, according to SDSU.
Orosz's colleague, SDSU astronomy professor William Welsh, presented the findings to the International Astronomical Union meeting in Beijing, China.
"The thing I find most exciting is the potential for habitability in a circumbinary system," Welsh said. "Kepler-47c is not likely to harbor life, but if it had large moons, those would be very interesting worlds."
The phenomenon recalls what was a visually stunning scene in the original "Star Wars" film, in which Luke Skywalker went outside at dusk while two suns were setting.
The system of stars and planets were spotted by the Kepler space telescope. Since the planets are too far away to see, their presence was deduced by slight dips in brightness when they cross in front of their host stars. The telescope is sensitive enough to measure the data, according to Orosz.
"Each planet transits over the primary star, giving unambiguous evidence that the planets are real," Orosz said.
Planet b reduces light from the stars by 0.08 percent, while planet c causes a 0.2 percent reduction. Venus, in a recent transit in front of the sun, reduced its light by 0.1 percent.
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