About this world
Kepler-21 b is a super-Earth orbiting Kepler-21, a yellow-white F-type star (type F6IV) 354 light-years from Earth. It is about 1.6 times the size of Earth and holds 7.5 Earth masses. It completes an orbit every 2.79 days at 0.043 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 2,015 K (1,742 °C): far too hot for liquid water on its surface. By the "cosmic shoreline", its star has probably stripped its atmosphere away, leaving bare rock.
It was discovered in 2012 by transit with Kepler. A planet crosses its star and dims it by a tiny, periodic fraction.