Multiple Planets Orbiting Binary Stars

For the first time a multiple transiting planets orbiting binary suns has been discovered by NASA's Kepler Mission that is 4,900 light years away from Earth in the constellation Cygnus. The twin planets detected by the astronomers in the Kepler-47 system orbit around a pair of stars that eclipse each other every 7.5 days.

This discovery leads to the argument that more than one planet can form and exists in the binary star indicating the multiplicity of the planetary system in our galaxy. According to the astronomers both the stars differ from each other to a great extent, as one star is similar to the size of the sun which is just 84 percent as bright, while the second star is very small that makes up just one third of the size of the sun and is less than 1 percent 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 the outer planet kepler 47C orbits its host pair every 303 days which falls into the 'habitable zone'.

"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."

The planets are located far from each other which cannot be viewed by naked eye, and hence the researchers based their hunt for these transiting planets on the data provided by Keplers Space telescope, which measures the fall in the brightness of more than 15,0000 stars. Also the ground-based spectroscopic observations using telescopes helped to characterize the stellar properties.

"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."

Space.com quoted Orosz saying, "We think these planets and most other planets formed from a residual disk of debris left over from the star-formation process. It was not at all obvious that this disk could survive near a newly formed binary star, given the orbital motions of the two stars. However, it now appears that apart from minor differences in the orbital spacings, planetary systems around binary stars can be similar to those around single stars."