About this world
K2-17 b is a sub-Neptune orbiting K2-17, an orange dwarf (type K7) 408 light-years from Earth. It is about 2.2 times the size of Earth. It completes an orbit every 18 days at 0.12 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 487 K (214 °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 2015 by transit with K2. A planet crosses its star and dims it by a tiny, periodic fraction.