Kepler-217 and Its Three Planets

Kepler-217 is a star located 3600 light-years away. It is 2.63 billion years old, with a mass of 1.37 solar masses and a radius of 1.76 solar radii, making both its reported mass and radius estimates larger than the Sun's. Its temperature is 6340 K, hotter than the Sun's. Three planets are known to orbit this host: Kepler-217 b, Kepler-217 c, and Kepler-217 d. All three 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-217 b and Kepler-217 c were both discovered in 2014, while Kepler-217 d was discovered in 2016. Kepler-217 b is classified as a Super-Earth with a radius of 2.23 Earth radii, larger than Earth's, and it completes an orbit in 5.37 days. Kepler-217 c is also a Super-Earth, with a radius of 1.85 Earth radii, larger than Earth's, and an orbital period of 8.59 days. Kepler-217 d is classified as Earth-like, with a radius of 1.32 Earth radii, also larger than Earth's, and an orbital period of 3.89 days.

Among the listed planets, Kepler-217 d has the shortest reported year, at 3.89 days, and the smallest reported radius, at 1.32 Earth radii. Kepler-217 b has the largest reported radius, at 2.23 Earth radii, and the second-shortest reported year, at 5.37 days. Kepler-217 c has the longest reported year, at 8.59 days, and the second-smallest reported radius, at 1.85 Earth radii.