Kepler-47: A Two-Star System With Three Known Planets

Kepler-47 is a binary star system 3340 light-years from Earth. Its selected host star has a mass of 1.05 solar masses, a radius of 0.963 solar radii, and a temperature of 5640 K. The star's reported radius estimate is smaller than the Sun's, and its reported temperature is cooler than the Sun's. Three planets are known to orbit this host.

All three planets are circumbinary, meaning they orbit both stars of the binary system rather than one star alone. They were all found by the transit method, in which a planet passes in front of its star from our viewpoint and causes a small dip in observed brightness; repeated dips help establish orbital periods.

Kepler-47 b, discovered in 2012, is Neptune-like, with a radius of 3.05 Earth radii. Its radius estimate is larger than Earth's, and its mean density is 0.402 g/cm³, 0.073 times Earth's. It has a mass of 2.07 Earth masses and an orbital period of 49.5 days. Among the listed planets, it has the shortest year and the smallest radius and reported mass.

Kepler-47 c, also discovered in 2012, is Jupiter-like, with a radius of 4.65 Earth radii. Its radius and mass estimates are larger than Earth's, and its mean density is 0.174 g/cm³, 0.0315 times Earth's. It has a mass of 3.17 Earth masses and an orbital period of 303 days. Among the listed planets, it has the longest year, the second-smallest radius, and the second-smallest reported mass.

Kepler-47 d, discovered in 2019, is Jupiter-like, with a radius of 7.04 Earth radii. Its radius and mass estimates are larger than Earth's, and its mean density is 0.3 g/cm³, 0.0545 times Earth's. It has a mass of 19 Earth masses and an orbital period of 187 days. Among the listed planets, it has the second-shortest year, the largest radius, and the largest reported mass.