NASA's Kepler mission has
discovered the first transiting circumbinary system -- multiple planets
orbiting two suns -- 4,900 light-years from Earth, in the constellation
Cygnus, proving that more than one planets can form and survive in orbit
around a binary star. The inner planet, Kepler-47b, orbits the pair of
stars in less than 50 days. It is thought to be a sweltering world,
where the destruction of methane in its super-heated atmosphere might
lead to a thick haze that could blanket the planet. At three times the
radius of Earth, Kepler-47b is the smallest known transiting
circumbinary planet. The outer planet, Kepler-47c, orbits its host pair
every 303 days, placing it in the so-called 'habitable zone,' the region
in a planetary system where liquid water might exist on the surface of a
planet. While not a world hospitable for life, Kepler-47c is thought to
be a gaseous giant, slightly larger than Neptune, where an atmosphere
of thick bright water clouds might exist.