The Kepler-24 System: Four Worlds Around a Star

Kepler-24 is a star 3770 light-years away, and four planets have been found orbiting it. The host star is 7.7 billion years old, holds 1.03 solar masses, spans 1.07 solar radii, and has a temperature of 5800 K. All four planets were detected 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.

Among the listed planets, Kepler-24 d has the shortest year by reported estimates: this Super-Earth has a radius of 1.67 Earth radii and an orbital period of 4.24 days. Kepler-24 b, also a Super-Earth, has a radius of 2.35 Earth radii, a mass of 11.1 Earth masses, and an orbital period of 8.14 days, the second-shortest among the listed planets. Its mean density is 4.74 g/cm³, 0.861 times Earth's.

Kepler-24 c, a Neptune-like planet, has a radius of 2.51 Earth radii, a mass of 9.99 Earth masses, and an orbital period of 12.3 days, the second-longest among the listed planets. Its mean density is 3.46 g/cm³, 0.629 times Earth's. Kepler-24 e has the longest year by reported estimates among the listed planets: this Neptune-like planet has a radius of 2.78 Earth radii, the largest among the listed planets, and an orbital period of 19 days.

In size-class terms, which compare radius with Earth's, a Super-Earth reaches 2.5 times Earth's radius and a Neptune-like planet reaches 4 times. The radii of Kepler-24 b, Kepler-24 c, Kepler-24 d, and Kepler-24 e are all larger than Earth's, as are the reported masses of Kepler-24 b and Kepler-24 c. Kepler-24 d has the smallest radius among the listed planets, while Kepler-24 e has the largest. Kepler-24 b's radius is the second-smallest listed, and Kepler-24 c's is the second-largest. The 2011 discoveries were Kepler-24 b and Kepler-24 c; Kepler-24 d and Kepler-24 e followed in 2014.