About this world
Kepler-309 c is a sub-Neptune orbiting Kepler-309, a cool red dwarf (type M0V) 1.78 thousand light-years from Earth. It is about 2.5 times the size of Earth. It completes an orbit every 105 days at 0.4 AU from its star.
Its equilibrium temperature is about 204 K (−69 °C): too cold for liquid water on its surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2014 by transit with Kepler. A planet crosses its star and dims it by a tiny, periodic fraction. Kepler-309 has 2 known planets; the others are Kepler-309 b.