Kepler 47: First Multi-circumbinary Planet System

Abstract

The eclipsing binary Kepler-47 is the first system detected to have multiple ▶ circumbinary planets (Orosz et al. 2012). The binary consists of a Sun-like star and a companion roughly one-third its size, orbiting each other every 7.45 days. The planets were detected using transit photometry when each planet transits the stars of the binary. Figure 1 shows some of the planetary transits of this system. The inner and outer planets of Kepler-47 system have radii 3.0 and 4.6 times that of Earth, respectively. The inner planet, Kepler-47b, has an orbital period of 49.5 days. The outer planet’s orbital period is 303.2 days. Calculation of the ▶Habitable Zone (HZ) of the Kepler-47 binary by Haghighipour and Kaltenegger (2013) has shown that the outer planet, Kepler-47c, is in the binary Habitable Zone (Fig. 2). Since this planet is larger than Earth, it cannot be habitable. However, it can have natural moons that could be habitable. A movie of the evolution of the Habitable zone of this system can be found at http://astro.twam. info/hz-ptype/. The detection of the Kepler-47 planetary system as the first with multiple planets in circumbinary orbits establishes that close binary stars can host complete (and even habitable) planetary systems. Figure 3 shows an artist’s rendering of this system.