Kepler-16b

Kepler-16b (formally Kepler-16 (AB)-b) is a Saturn-sized exoplanet consisting of half gas and half rock and ice. It orbits a binary star, Kepler-16, with a period of 229 days. "It is the first confirmed, unambiguous example of a circumbinary planet – a planet orbiting not one, but two stars," said Josh Carter of the Center for Astrophysics | Harvard & Smithsonian, one of the discovery team. Kepler-16b is also unusual in that it falls inside the radius that was thought to be the inner limit for planet formation in a binary star system. According to Sara Seager, a planetary expert at the Massachusetts Institute of Technology, it was thought that for a planet to have a stable orbit around such a system, it would need to be at least seven times as far from the stars as the stars are from each other. Kepler-16b's orbit is only about half that distance. Kepler-16b orbits near the outer edge of the habitable zone, but it is a gas giant with surface temperatures around −100 to −70 °C (−150 to −94 °F).