Spotted using data from the Kepler space telescope, the gas giant, dubbed Kepler-1647b, has one of the longest orbits recorded for a transiting planet

A gas giant 3,700 light years away is the largest planet yet to be found orbiting two stars, scientists have revealed.

Dubbed Kepler-1647b, the Jupiter-like planet lies in the constellation Cygnus, and was spotted by astronomers examining data from the Kepler space telescope - an instrument launched in 2009 to look for potentially habitable planets beyond our solar system.

Not only is it the largest “circumbinary” planet, it also has one of the longest orbits ever recorded for a transiting planet, taking 1,107 days to complete its circuit.

But it isn’t the only body on the move. As Kepler-1647b travels around the system, the two stars are, themselves, in orbit around each other.

“Every 11 days the stars eclipse each other, so it is like a clock,” said Veselin Kostov, lead author of the new research from Nasa’s Goddard Space Flight Center.

For an observer watching from Kepler-1647b, that could lead to an intriguing spectacle.



“Sometimes one will be able to see first the larger star rise or set followed by the smaller one,” said Tobias Cornelius Hinse, a co-author of the research from the Korea Astronomy and Space Science Institute. “But, under special circumstances, one could also imagine [seeing] only one star setting or rising, when the smaller star is hiding behind the larger one during sunrise or sunset.”

Presented at a meeting of the American Astronomical Society by an international team of scientists, the research is based on data from the Kepler space telescope, together with a host of ground-based measurements and computer models.

Facebook Twitter Pinterest Comparison of the relative sizes of several Kepler circumbinary planets, from the smallest, Kepler-47 b, to the largest, the newly-discovered Kepler-1647 b. Illustration: Lynette Cook

The team found that, like Luke Skywalker’s home planet of Tatooine, Kepler-1647b orbits two stars, making it the 11th such planet to be discovered by using the Kepler space telescope. While one of the stars is slightly smaller than our sun the other is larger, its mass 20% greater.

As the two stars orbit each other, their light dims - an event picked up by the Kepler space telescope. Similarly, when a planet passes in front of the stars, a smaller dip in light intensity can be spotted. “You can imagine if you move something dark across something very bright, the amount of light [detected] will decrease a tiny little bit,” said Kostov.

But, he added, at just over three Earth-years long, the orbit of Kepler-1647b made the planet’s detection challenging: with the Kepler space telescope observing the stars during a four-year period, only three transits were seen. “In the first occurrence, it transited only one of the stars, and then three years later it transited both of them,” he said.

Together with ground-based observations from made by both professional and amateur astronomers, the team concluded that the two stars orbit each other every 11 days. Kepler-1647b was found to orbit the two-star system every 1,107 days at 2.7 times the distance of the Earth from our sun. The long orbit of the Kepler-1647b compared to similar previously observed planets, says Hinse, backs up the theory that such planets form at large distances from their stars and then spiral in towards them.



The team also found that Kepler-1647b falls within the “habitable” zone of the double-sun system - the distance from the stars at which it is possible for liquid water to be present. Not that Kepler-1647b is likely to harbour life as we know it - the planet was found to be a gas giant of a similar size to Jupiter.

But Hinse believes there could be other possibilities. “One potential place to have life in this system would be if Kepler-1647b is being orbited by a moon - because that moon would always be in the habitable zone,” he said.

What’s more he adds, his calculations have thrown up another avenue to explore. “There is actually a region between the [two stars] and the planet [Kepler-1647b] where you can have an Earth-like planet on a stable orbit for billions of years,” said Hinse. “We didn’t detect it, but it is possible.”

According to Kostov, the hunt for planets outside our solar system is set to become even more exciting. Next year will see the launch of Nasa’s Transiting Exoplanet Survey Satellite (TESS) - an instrument that will monitor hundreds of thousands of stars for signs of orbiting planets.



“There are plenty of mysteries,” said Kostov. “We are just touching the tip of the iceberg now.”

