Kepler-257: A Distant Star with Three Giant Worlds

Kepler-257 is a star located 2540 light-years away. It has a reported age of 4.79 billion years, a mass of 0.85 solar masses, a radius of 0.81 solar radii, and a temperature of 5210 K. Its mass and radius are smaller than the Sun's, and its temperature is cooler. Three planets orbit this host.

All three planets were discovered by transit in 2014. A transit occurs when a planet passes in front of its star from our viewpoint, causing a small dip in observed brightness. Repeated dips help establish orbital periods.

Kepler-257 b is classified as Neptune-like. It has an orbital period of 2.38 days and a radius of 2.61 Earth radii, which is larger than Earth's. Among the listed planets, it has the shortest year and the smallest radius. Kepler-257 c is Jupiter-like, with an orbital period of 6.58 days and a radius of 5.41 Earth radii. Its radius is larger than Earth's, and among the listed planets it has the second-shortest year and the largest radius. Kepler-257 d is also Jupiter-like, with an orbital period of 24.7 days and a radius of 4.95 Earth radii, larger than Earth's. Among the listed planets, it has the longest year and the second-smallest radius.