About this world
Kepler-398 d is an Earth-sized planet orbiting Kepler-398, an orange dwarf 578 light-years from Earth. It is about 0.88 times the size of Earth. It completes an orbit every 6.83 days at 0.062 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 636 K (363 °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 2016 by transit with Kepler. A planet crosses its star and dims it by a tiny, periodic fraction. Kepler-398 has 3 known planets; the others are Kepler-398 b and Kepler-398 c.