Kepler-102: A Compact Five-Planet System

Kepler-102 is a star located 352 light-years away, and five planets have been identified orbiting it. The host star is 0.8 solar masses with a radius of 0.74 solar radii, making it smaller than the Sun in both respects. Its temperature of 4900 K is cooler than the Sun's, and its age is 1.41 billion years.

All five 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. Kepler-102 b, c, and f are Sub-Earths, a size class for planets smaller than Earth. Kepler-102 b has a radius of 0.46 Earth radii, a reported upper limit of 1.1 Earth masses, and an orbital period of 5.29 days, the shortest among the listed planets. Kepler-102 c has a radius of 0.567 Earth radii, a reported upper limit of 1.7 Earth masses, and a period of 7.07 days, the second-shortest among the listed planets. Kepler-102 f has a radius of 0.861 Earth radii, a reported upper limit of 4.3 Earth masses, and a period of 27.5 days, the longest among the listed planets. Each of these three radii is smaller than Earth's.

Kepler-102 d is classified as Earth-like, a size class for planets within 1.5 times Earth's radius. It has a radius of 1.15 Earth radii and a mass of 3 Earth masses, both larger than Earth's, with an orbital period of 10.3 days. Its mean density is 10.8 g/cm³, 1.95 times Earth's, and its radius is the second-largest among the listed planets. Kepler-102 e is a Super-Earth, a size class for planets reaching 2.5 times Earth's radius. It has a radius of 2.17 Earth radii, the largest among the listed planets, and a mass of 4.7 Earth masses, larger than Earth's. Its orbital period is 16.1 days, the second-longest among the listed planets, and its mean density is 2.53 g/cm³, 0.46 times Earth's.