Kepler-42 and Its Three Small Worlds

Kepler-42 is a single-star system 131 light-years away, and three planets orbit the host. The star is an M-type dwarf with a reported mass estimate of 0.13 solar masses, a reported radius estimate of 0.17 solar radii, and a reported temperature of 3070 K. Its reported age has a lower limit of 4.5 billion years. The star's reported mass and radius estimates are smaller than the Sun's, and its reported temperature is cooler than the Sun's.

All three planets were discovered by transit in 2011 and are classified as Sub-Earths, meaning their radii are smaller than Earth's. Kepler-42 b has a radius of 0.78 Earth radii and an orbital period of 1.21 days. Kepler-42 c has a radius of 0.73 Earth radii and an orbital period of 0.453 days, the shortest year among the listed planets. Kepler-42 d has a radius of 0.57 Earth radii and an orbital period of 1.87 days, the longest year among the listed planets, and it has the smallest radius among the listed planets. Kepler-42 b has the largest radius among the listed planets, while Kepler-42 c has the second-shortest year and the second-smallest radius among them. The reported radius estimates of Kepler-42 c and Kepler-42 d are smaller than Earth's.