Kepler-1542 and Its Four Sub-Earth Planets

Kepler-1542 is a star located 1300 light-years away, and four planets have been identified orbiting it. All four were discovered by transit, 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 star is 8.51 billion years old and has a mass of 0.94 solar masses, a radius of 0.99 solar radii, and a temperature of 5560 K. Its reported mass estimate is smaller than the Sun's, and its reported temperature is cooler than the Sun's.

The planets are Kepler-1542 b, Kepler-1542 c, Kepler-1542 d, and Kepler-1542 e. Each is classified as a Sub-Earth, a size class for planets smaller than Earth. Their reported radius estimates are correspondingly smaller than Earth's: Kepler-1542 b and Kepler-1542 e each have a radius of 0.76 Earth radii, Kepler-1542 c has a radius of 0.65 Earth radii, and Kepler-1542 d has a radius of 0.87 Earth radii. Among the listed planets, Kepler-1542 c has the smallest radius by reported estimates, while Kepler-1542 d has the largest.

The planets complete their orbits in just a few days. Kepler-1542 c has an orbital period of 2.89 days, Kepler-1542 b has one of 3.95 days, Kepler-1542 e has one of 5.1 days, and Kepler-1542 d has one of 5.99 days. Among the listed planets, Kepler-1542 c has the shortest year by reported estimates, and Kepler-1542 d has the longest; Kepler-1542 b has the second-shortest year, and Kepler-1542 e has the second-longest.