Kepler-178: A Distant Star With Three Neptune-Like Worlds

Kepler-178 is a star located 2340 light-years away. It is 4.68 billion years old, with a mass of 0.94 solar masses and a radius of 0.92 solar radii. Its temperature is 5540 K, and its reported mass estimate is smaller than the Sun's, while its reported temperature is cooler than the Sun's. Three planets are known to orbit this host.

All three planets were discovered in 2014 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. Kepler-178 b, Kepler-178 c, and Kepler-178 d are all Neptune-like, a size class that reaches 4 times Earth's radius. Each has a reported radius estimate larger than Earth's.

Kepler-178 b has an orbital period of 9.58 days and a radius of 2.9 Earth radii. Among the listed planets, it has the shortest year by reported estimates, at 9.58 days, and the second-smallest radius by reported estimates, at 2.9 Earth radii. Kepler-178 c has an orbital period of 20.6 days and a radius of 2.88 Earth radii. Among the listed planets, it has the second-shortest year by reported estimates, at 20.6 days, and the smallest radius by reported estimates, at 2.88 Earth radii. Kepler-178 d has an orbital period of 96.7 days and a radius of 3.95 Earth radii. Among the listed planets, it has the longest year by reported estimates, at 96.7 days, and the largest radius by reported estimates, at 3.95 Earth radii.