K2-19: A Sun-Like Star and Its Three Transiting Planets

K2-19 is a G9 star located 945 light-years away, with three planets orbiting it. The host star is estimated to be 1.7 billion years old, with a reported mass of 0.892 solar masses, a radius of 0.824 solar radii, and a temperature of 5350 K. Its mass and radius are both smaller than the Sun's, and its temperature is cooler.

All three planets were found by the transit method, in which a planet passing in front of its star from our viewpoint causes a small dip in observed brightness. K2-19 b and K2-19 c were both discovered in 2015 and are Jupiter-like in size. K2-19 b has a mass of 30.8 Earth masses, a radius of 7 Earth radii, and an orbital period of 7.92 days. K2-19 c has a mass of 11 Earth masses, a radius of 4.1 Earth radii, and an orbital period of 11.9 days. Both are larger in radius and more massive than Earth. Their estimated mean densities are 0.495 g/cm³, or 0.0898 times Earth's, for K2-19 b, and 0.879 g/cm³, or 0.16 times Earth's, for K2-19 c.

K2-19 d, discovered in 2016, is Earth-like, with a radius of 1.04 Earth radii and an orbital period of 2.51 days. Its mass is reported as an upper limit of 6.2 Earth masses. Among the listed planets, K2-19 d has the shortest year by reported estimates, at 2.51 days; K2-19 b has the second-shortest, at 7.92 days; and K2-19 c has the longest, at 11.9 days. K2-19 d also has the smallest radius among the listed planets, while K2-19 b has the largest and K2-19 c the second-smallest.