Kepler-128: A Star and Its Two Known Planets

Kepler-128 is a star located 1,290 light-years away. It is 4.07 billion years old and has a mass of 1.22 solar masses and a radius of 1.7 solar radii, both larger than the Sun's corresponding values. Its temperature of 6,140 K is also hotter than the Sun's. Two planets are known to orbit this star.

Both planets were discovered in 2013 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-128 b is an Earth-like planet with a mass of 3.79 Earth masses and a radius of 1.42 Earth radii, both larger than Earth's. Its mean density is 7.28 g/cm³, 1.32 times Earth's. It completes an orbit every 15 days.

Kepler-128 c is a Super-Earth with a mass of 3.38 Earth masses and a radius of 1.52 Earth radii, again larger than Earth's. Its mean density is 5.29 g/cm³, 0.961 times Earth's. Its orbital period is 22.8 days.

Among the listed planets, Kepler-128 b has the shortest year by reported estimates, while Kepler-128 c has the longest. Kepler-128 b also has the smallest radius, and Kepler-128 c the largest. Kepler-128 b has the largest reported mass, while Kepler-128 c has the smallest.