Scientists discover a giant planet that orbits two suns

Some worlds have more than one sun in their sky. Now scientists say they've confirmed the existence of the largest-ever planet orbiting a pair of binary stars - a gas giant with the same mass and radius as Jupiter.

Exoplanets such as this one - situated in their stars' habitable zone and massive enough to lasso in many rocky moons - could be an interesting place to go looking for signs of alien life.

The newly confirmed behemoth has been dubbed Kepler-1647 b, and it sits 3,700 light-years away in the constellation Cygnus. At an estimated 4.4 billion years old, it's roughly the same age as Earth. But it's nothing like our home planet. It's what is known as a circumbinary world, one that orbits two suns that dance together as a binary pair. Its diameter is more than 11 times that of Earth's. Its suns are pretty similar to our own (one is slightly smaller and the other slightly larger).

At about 2.7 astronomical units (AUs) from its suns (Earth is 1 AU from ours) Kepler-1647 b is in the habitable zone of its stars. That means it's in the magic sweet spot that experiences the right amount of sunlight and heat to allow liquid water to form. But the planet itself wouldn't actually be home to life as we know it: It's almost entirely made of gas. If it's anything like the gas giants in our solar system, however, it probably has dozens of moons. And just like Saturn and Jupiter, those little rocky worlds could be great places to look for life like ours.

'Habitability aside, Kepler-1647 b is important because it is the tip of the iceberg of a theoretically predicted population of large, long-period circumbinary planets,” said study co-author William Welsh of San Diego State University.

Despite its size, the planet was difficult to pin down. Scientists find exoplanets by measuring the way the light of their host stars dim when the planets 'transit” or pass in front of stars, from our perspective. Kepler-1647 b has the longest orbit of any such planet ever detected.