The planet is six times the size of earth
Astronomers have found a planet whose skies are illuminated by four different suns - the first known of its type. The distant world orbits one pair of stars which have a second stellar pair revolving around them.The discovery was made by volunteers using the Planethunters.org website along with a team from UK and US institutes; follow-up observations were made with the Keck Observatory. The planet, located just under 5,000 light-years away, has been named PH1 after the Planet Hunters site.
It is thought to be a "gas giant" slightly larger than Neptune - more than six times the radius of the Earth.
All four stars pulling on it creates a very complicated environment. Yet there it sits in an apparently stable orbit. Astronomers are excited by this discovery and don't yet know how the planet manages to remain stable.
Binary stars - systems with pairs of stars - are not uncommon. But only a handful of known exoplanets (planets that circle other stars) have been found to orbit such binaries. And none of these binary star/planet systems are known to have another pair of stars circling them.
The Kepler Space Telescope
- Stares fixedly at a patch corresponding to 1/400th of the sky
- Looks at more than 155,000 stars
- Has so far found 2,321 candidate planets
- Among them are 207 Earth-sized planets, 10 of which are in the "habitable zone" where liquid water can exist
PH1 was discovered by two US volunteers using the Planethunters.org website: Kian Jek of San Francisco and Robert Gagliano from Cottonwood, Arizona. They spotted faint dips in light caused by the planet passing in front of its parent stars. The team of professional astronomers then confirmed the discovery using the Keck telescopes on Mauna Kea, Hawaii.
Founded in 2010, Planethunters.org aims to harness human pattern recognition to identify transits in publicly available data gathered by Nasa's Kepler Space Telescope. Kepler was launched in March 2009 to search for Earth-like planets orbiting other stars. Visitors to the Planet Hunters website have access to randomly selected data from one of Kepler's target stars. Volunteers are asked to draw boxes to mark the locations of visible transits - when a planet passes in front of its parent star.
Dr Lintott, member of the project, points out: "Computerized attempts to find things [in the data] missed this system entirely. That tells you there are probably more of these that are slipping through our fingers. We've just stuck a load of new data up on Planethunters.org to help people find the next one."
Searching for such systems, he said, was "a complicated test to hand a computer", adding: "We're using human pattern recognition, which can disentangle that reasonably well to see the important stuff." Since December 2010, more than 170,000 members of the public have participated in the project.