A team of citizen scientists and professional astronomers has discovered a circumbinary planet in a huge four-star system some 5,000 light years away.
This is an artist’s illustration of PH1 (Haven Giguere / Yale University)
The planet, dubbed PH1, was first identified by citizen scientists participating in Planet Hunters, a Yale-led program that enlists members of the public to review astronomical data from NASA’s Kepler spacecraft for signs of planets.
PH1 is a gas giant with a radius about 6.2 times that of Earth, making it a bit bigger than Neptune. Only six planets are known to orbit two stars and none of these are orbited by distant stellar companions.
“Circumbinary planets are the extremes of planet formation,” said Dr Meg Schwamb of Yale University, lead author of a paper to be published in the Astrophysical Journal (arXiv.org version). “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.”
This image shows a family portrait of the PH1 planetary system. The newly discovered planet is depicted in this artist’s rendition transiting the larger of the two eclipsing stars it orbits. Off in the distance, well beyond the planet orbit, resides a second pair of stars bound to the planetary system (Haven Giguere / Yale University)
The citizen scientists spotted faint dips in light caused by the planet as it passed in front of its parent stars, a common method of finding extrasolar planets. Dr Schwamb led the team of professional astronomers that confirmed the discovery and characterized the planet, following observations from the Keck telescopes on Mauna Kea, Hawaii.
This false color image shows KIC 4862625, a four-star system about 5,000 light years away (Megan E. Schwamb et al)
“Planet Hunters is a symbiotic project, pairing the discovery power of the people with follow-up by a team of astronomers,” said co-author Prof Debra Fischer of Yale University. “This unique system might have been entirely missed if not for the sharp eyes of the public.”
PH1 orbits outside the 20-day orbit of a pair of eclipsing stars (KIC 4862625) that are 1.5 and 0.41 times the mass of the Sun. The planet revolves around its host stars roughly every 138 days. Beyond the planet’s orbit at about 1000 AU is a second pair of stars orbiting the planetary system.
“The thousands of people who are involved with Planet Hunters are performing a valuable service,” said co-author Prof Jerome Orosz of San Diego State University. “Many of the automated techniques used to find interesting features in the Kepler data don’t always work as efficiently as we would like. The hard work of the Planet Hunters helps ensure that important discoveries are not falling through the cracks.”
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Bibliographic information: Megan E. Schwamb et al. 2012. Planet Hunters: A Transiting Circumbinary Planet in a Quadruple Star System. Submitted to ApJ; arXiv: 1210.3612
