Kepler-52: A Cool Dwarf and Its Three Super-Earths

Kepler-52 is an M0 V star located 1050 light-years away. M0 V is a spectral type, a classification of a star by temperature class and luminosity; an M-type dwarf is a small, cool red dwarf. The star’s reported mass estimate is 0.66 solar masses, smaller than the Sun’s. Its reported radius estimate is 0.63 solar radii, also smaller than the Sun’s, and its reported temperature is 4240 K, cooler than the Sun’s. Kepler-52 is 3.55 billion years old and hosts three planets.

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. Kepler-52 b and Kepler-52 c were discovered in 2012, and Kepler-52 d in 2014. Each is classified as a Super-Earth, meaning its radius reaches up to 2.5 times Earth's.

Kepler-52 b has a reported radius estimate of 2.1 Earth radii, larger than Earth’s, and a reported upper limit of 135 Earth masses. Its orbital period is 7.88 days, the shortest among the listed planets. Kepler-52 c has a reported radius estimate of 1.84 Earth radii, larger than Earth’s and the smallest among the listed planets, with a reported upper limit of 45.4 Earth masses. Its orbital period is 16.4 days, the second-shortest among the listed planets. Kepler-52 d has a reported radius estimate of 1.95 Earth radii, larger than Earth’s and the second-smallest among the listed planets, and an orbital period of 36.4 days, the longest among the listed planets. No mass estimate is reported for Kepler-52 d.