Saturday 24 November 2012

Citizen scientists discover a sub-Jovian planet in a quaternary star system.

The Planet Hunters is a citizen science project (i.e. a science project carried out largely by members of the public) which asks visitors to a website to look at randomly selected 30 light-curves from the Kepler Space Telescope, and look for patterns. Volunteers who find patterns that may indicate planets can flag these up for investigation by astronomers.

In a paper published on the online arXiv database at Cornell University Library on 12 October 2012, a team of scientists led by Megan Schwamb of the Yale Center for Astronomy and Astrophysics and the Department of Physics at Yale University describe the first planet discovered by the Planet Hunters project, a sub-Jovian planet in the KIC 4862625 star system (Kepler Input Catalogue 4862625), roughly 5000 light years from Earth in the constellation of Cygnus.

The planet, named PH1, has a maximum possible mass 169 times that of the Earth, slightly over half the mass of Jupiter but considerably larger than Saturn. It orbits a binary pair of stars, named Aa and Ab, every 138 days at a distance of 0.634 AU (63.4% of the distance at which the Earth orbits the Sun). The larger of these two stars Aa, is an F-type yellow-white star, with a mass of 1.5 times the mass of the Sun. This is orbited by a smaller, M-type red dwarf star with a mass 0.4 times that of the Sun every 20 days at a distance of 0.17 AU. All of these components eclipse (pass in front of) one-another when seen from our Solar System.

Diagram showing the relative positions of PH1, Aa and Ab in the inner part of the KIC 4862625 system. Shwamb et al. (2012).

Orbiting this system at a distance of roughly 1000 AU is a second pair of binary stars, detected by their gravitational influence upon the primary binary. These are named Ba and Bb, Ba probably being a G-type yellow dwarf star with 99% of the mass of our Sun and Bb probably being a M-type red dwarf star with a mass 51% if the Sun's.

The whole system is thought to be about 2 billion years old, compared to about 4.5 billion years for our Solar System.

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