K2-199: A Nearby Star With Two Short-Period Planets

K2-199 is a star located 351 light-years away, and two planets have been cataloged in orbit around it. The star is estimated to be 5.04 billion years old, with a mass of 0.711 solar masses and a radius of 0.682 solar radii. Its reported temperature is 4490 K. Compared with the Sun, the star's reported mass, radius, and temperature estimates are all smaller or cooler.

The first planet, K2-199 b, was discovered in 2018 by the transit method. This classifies it as a Super-Earth, a size class that compares radius with Earth's. It has a mass of 6.9 Earth masses and a radius of 1.73 Earth radii, both larger than Earth's corresponding values, and a mean density of 7.34 g/cm³, which is 1.33 times Earth's. Its orbital period is 3.23 days.

K2-199 c was also discovered in 2018 by the transit method. It is classified as Neptune-like, a size class that also compares radius with Earth's. It has a mass of 12.4 Earth masses and a radius of 2.85 Earth radii, both larger than Earth's. Its mean density is 2.95 g/cm³, which is 0.536 times Earth's. Its orbital period is 7.37 days.

Among the listed planets, K2-199 b has the shortest year, at 3.23 days, as well as the smallest radius, at 1.73 Earth radii, and the smallest reported mass, at 6.9 Earth masses. K2-199 c has the longest year, at 7.37 days, along with the largest radius, at 2.85 Earth radii, and the largest reported mass, at 12.4 Earth masses. A transit occurs when a planet passes in front of its star from our viewpoint, causing a small dip in observed brightness; repeated dips help establish orbital periods, and both planets here were found that way.