About this world
K2-331 c is a sub-Neptune orbiting K2-331, a yellow, Sun-like star 690 light-years from Earth. It is about 2.7 times the size of Earth. It completes an orbit every 23 days at 0.16 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 673 K (400 °C): far too hot for liquid water on its surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2021 by transit with K2. A planet crosses its star and dims it by a tiny, periodic fraction. K2-331 has 2 known planets; the others are K2-331 b.