Two amateur astronomers have discovered the first example of a planet orbiting twin suns that is itself orbited by a second distant pair of stars.
A team of volunteers using the Planethunters.org website, along with professional astronomers, confirmed the discovery of the phenomenon, called a circumbinary planet in a four-star system.
Only six planets are known to orbit two stars, according to researchers, and none of these are orbited by distant stellar companions.
"Circumbinary planets are the extremes of planet formation," says 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."
Dubbed PH1, the planet was first identified by two volunteers, marking Planet Hunters' first confirmed planet discovery.
Kian Jek of San Francisco and Robert Gagliano of Cottonwood, Arizona were the first to spot faint dips in light caused by the planet - dubbed PH1 - as it passed in front of its parent stars. Follow-up observations showed it to be a gas giant with a radius about 6.2 times that of Earth, making it a bit bigger than Neptune.
PH1 orbits outside the 20-day orbit of a pair of eclipsing stars that are 1.5 and 0.41 times the mass of the sun. It revolves around its host stars roughly every 138 days. Beyond the planet's orbit, at about 1,000 times the distance between Earth and the sun, is a second pair of stars orbiting the planetary system.
"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," says Jek.