A GROUP of amateur astronomers have helped scientists discover something never seen before: a planet with four suns.
Volunteers from the Planethunters.org website teamed up with an international alliance of astronomers led from Yale University, in search of new planets orbiting distant stars.
They discovered a so-far unique interstellar oddity: a planet orbiting twin suns that in turn is orbited by a second, more distant pair of stars.
There only six planets known to orbit two stars - and none have ever been seen with four, the researchers say.
A paper about the new star system was presented on Monday at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Reno, Nevada, and has been submitted for publication.
"Circumbinary planets are the extremes of planet formation," said Meg Schwamb of Yale. "The discovery of these systems is forcing us to go back to the drawing board to understand how such planets can assemble and evolve in these dynamically challenging environments."
The new planet, dubbed PH1, was first identified by citizen scientists in the Planet Hunters program. The program enlists amateurs to scour data from NASA's Kepler spacecraft for the telltale momentary dip in a star's brightness that is the sign of a planet crossing in front of the star.
Two volunteers, one from San Francisco and another from Arizona, spotted the planet and the discovery was then confirmed by professionals at the Keck telescopes on top of Mauna Kea in Hawaii.
PH1, a gas giant with a radius about six times that of Earth - with half the mass of Jupiter - orbits around a pair of stars locked in a tight embrace. One star is 50 per cent bigger than our Sun, the other a bit less than half the size of our Sun.
Then, much further out, another pair of stars also orbit the central pair.
The system is about 5000 light-years away.
Kian Jek, one of the amaetur sleuths who spotted the planet, said he was still in awe of the discovery. "It still continues to astonish me how we can detect, let alone glean so much information about another planet thousands of light years away just by studying the light from its parent star," he said.