About this world
Kepler-18 d is a Neptune-like planet orbiting Kepler-18, a yellow, Sun-like star 1.41 thousand light-years from Earth. It is about 0.62 times the size of Jupiter and holds 0.052 Jupiter masses. It completes an orbit every 14.9 days at 0.12 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 720 K (447 °C): far too hot for liquid water on its surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium. Its atmosphere has already been studied: 2 spectroscopic observations.
It was discovered in 2011 by transit with Kepler. A planet crosses its star and dims it by a tiny, periodic fraction. Kepler-18 has 3 known planets; the others are Kepler-18 b and Kepler-18 c.