Kepler-198: A Star and Its Three Planets

Kepler-198 is a star located 1620 light-years away, and three planets orbit it. The star is 3.72 billion years old and contains 0.97 solar masses. Its radius is 0.93 solar radii, smaller than the Sun's, and its surface temperature is 5640 K, cooler than the Sun's. All three planets were 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, the time each planet takes to complete one orbit.

Kepler-198 b is a Neptune-like planet discovered in 2014. It has an orbital period of 17.8 days and a radius of 2.82 Earth radii, larger than Earth's. Kepler-198 c, a Super-Earth discovered in 2014, orbits once every 49.6 days and has a radius of 2.47 Earth radii, also larger than Earth's. Kepler-198 d, another Super-Earth, was discovered in 2016. Its orbital period is 1.31 days, and its radius is 1.53 Earth radii, larger than Earth's as well.

Among these listed planets, Kepler-198 b has the largest radius, at 2.82 Earth radii, while Kepler-198 d has the smallest, at 1.53 Earth radii. Kepler-198 d also has the shortest orbital period, at 1.31 days, whereas Kepler-198 c has the longest, at 49.6 days. Kepler-198 b falls between them with the second-shortest orbital period, at 17.8 days.