Kepler-253: A Distant Star With Three Known Planets

Kepler-253 is a star located 2740 light-years away, and three planets have been found orbiting it. The star's reported mass estimate is 0.85 solar masses, smaller than the Sun's, and its reported radius estimate is 0.81 solar radii, also smaller than the Sun's. Its reported temperature is 5220 K, cooler than the Sun's, and its age is 4.57 billion years.

The three planets are Kepler-253 b, Kepler-253 c, and Kepler-253 d. All three were discovered by transit in 2014, the 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 a planet takes to complete one orbit.

Kepler-253 b is a Super-Earth with an orbital period of 3.78 days and a radius of 1.63 Earth radii, the smallest radius and shortest year among the listed planets. Kepler-253 c is Neptune-like, with an orbital period of 10.3 days and a radius of 2.65 Earth radii; this is the second-shortest year and second-smallest radius among the listed planets. Kepler-253 d is also Neptune-like, with an orbital period of 18.1 days and a radius of 3.17 Earth radii, the largest radius and longest year among the listed planets. Kepler-253 c's and Kepler-253 d's reported radius estimates are larger than Earth's.