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NASA's Kepler Discovers Multiple Planets Orbiting a Pair of Stars
by Staff Writers
Washington DC (SPX) Sep 03, 2012


The planets Kepler-47b and Kepler-47c: Kepler-47b has three times the radius of earth and orbits the pair of stars in less than 50 days while Kepler-47c is thought to be a gaseous giant, slightly larger than Neptune with an orbital period of 303 days. Credit: NASA/JPL-Caltech/T. Pyle. For a larger version of this image please go here.

Coming less than a year after the announcement of the first circumbinary planet, Kepler-16b, NASA's Kepler mission has discovered multiple transiting planets orbiting two suns for the first time. This system, known as a circumbinary planetary system, is 4,900 light-years from Earth in the constellation Cygnus.

This discovery proves that more than one planet can form and persist in the stressful realm of a binary star and demonstrates the diversity of planetary systems in our galaxy.

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.

"In contrast to a single planet orbiting a single star, the planet in a circumbinary system must transit a 'moving target.' As a consequence, time intervals between the transits and their durations can vary substantially, sometimes short, other times long," said Jerome Orosz, associate professor of astronomy at San Diego State University and lead author of the paper.

"The intervals were the telltale sign these planets are in circumbinary orbits."

The inner planet, Kepler-47b, orbits the pair of stars in less than 50 days. While it cannot be directly viewed, it is thought to be a sweltering world, where the destruction of methane in its super-heated atmosphere might lead to a thick haze that could blanket the planet.

At three times the radius of Earth, Kepler-47b is the smallest known transiting circumbinary planet.

The outer planet, Kepler-47c, orbits its host pair every 303 days, placing it in the so-called "habitable zone," the region in a planetary system where liquid water might exist on the surface of a planet. While not a world hospitable for life, Kepler-47c is thought to be a gaseous giant slightly larger than Neptune, where an atmosphere of thick bright water-vapor clouds might exist.

"Unlike our sun, many stars are part of multiple-star systems where two or more stars orbit one another. The question always has been - do they have planets and planetary systems? This Kepler discovery proves that they do," said William Borucki, Kepler mission principal investigator at NASA's Ames Research Center in Moffett Field, Calif.

"In our search for habitable planets, we have found more opportunities for life to exist."

To search for transiting planets, the research team used data from the Kepler space telescope, which measures dips in the brightness of more than 150,000 stars. Additional ground-based spectroscopic observations using telescopes at the McDonald Observatory at the University of Texas at Austin helped characterize the stellar properties. The findings are published in the journal Science.

"The presence of a full-fledged circumbinary planetary system orbiting Kepler-47 is an amazing discovery," said Greg Laughlin, professor of Astrophysics and Planetary Science at the University of California in Santa Cruz.

"These planets are very difficult to form using the currently accepted paradigm, and I believe that theorists, myself included, will be going back to the drawing board to try to improve our understanding of how planets are assembled in dusty circumbinary disks."

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Related Links
Kepler at NASA
Lands Beyond Beyond - extra solar planets - news and science
Life Beyond Earth






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EXO WORLDS
Kepler discovers planetary system orbiting 2 suns
San Diego CA (SPX) Aug 31, 2012
Astronomers at the International Astronomical Union meeting announced the discovery of the first transiting circumbinary multi-planet system: two planets orbiting around a pair of stars. The discovery shows that planetary systems can form and survive even in the chaotic environment around a binary star. And such planets can exist in the habitable zone of their stars. "Each planet transits ... read more


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