Kepler-57: A Cool Dwarf with Two Transiting Worlds

Kepler-57 is a star located 2100 light-years away, and two planets have been found orbiting it. Both worlds 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. The host star is 4.68 billion years old and has a mass of 0.88 solar masses and a radius of 0.84 solar radii, both smaller than the Sun's. Its temperature is 5390 K, cooler than the Sun's.

Kepler-57 b is a Neptune-like planet discovered in 2012, with a radius of 3.14 Earth radii and a mass of 25.1 Earth masses, both larger than Earth's. Its mean density is 4.48 g/cm³, 0.813 times Earth's. It completes one orbit every 5.72 days, the shortest year among the listed planets.

Kepler-57 c is a Super-Earth discovered in 2012, with a radius of 2.2 Earth radii and a mass of 6.86 Earth masses, both larger than Earth's. Its mean density is 3.57 g/cm³, 0.648 times Earth's. Its orbital period is 11.6 days, the longest year among the listed planets, and it has both the smallest radius and the smallest reported mass of the two worlds.