NASA's Kepler mission has discovered multiple planets orbiting a pair of stars for the first time, showing evidence for the presence of circumbinary planetary system.

Researchers analyzed the data collected by the Kepler telescope to find the presence of  transiting planets. The announcement has come just less than a year after the Kepler mission found a circumbinary planet named Kepler-16b that orbits two stars instead of one.

Astronomers found two planets orbiting a pair of stars in the Kepler-47 system that overshadows each other every 7.5 days from the NASA's preferred point on Earth.  One of the stars was found to be around the same size as that of the sun with 84 percentage of brightness, the other star was found be around one-third of the size of the sun with less than one percent brightness.

"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," Jerome Orosz, associate professor of astronomy at San Diego State University and lead author of the paper, said in a statement.

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

While the inner planet named as Kepler-47b orbits around the pair of stars in 50 days, the outer planet Kepler-47c orbits them in 303 days.  

The inner planet which is at three times the radius of Earth is the smallest transiting circumbinary planet found. It is said to have a hot atmosphere which is not habitable, where methane destruction could possibly form a blanket on the planet.

But NASA astronomers have placed Kepler-47c in the habitable zone, where liquid water might possibly be present. They pointed out that the planet is friendly to support life. The planet is slightly bigger than the size of Neptune and might have water-vapor clouds in its atmosphere.

"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," Greg Laughlin, professor of Astrophysics and Planetary Science at the University of California in Santa Cruz, said in a statement.

The findings of the study are published in the Aug. 28 issue of the journal Science.