About this world
Kepler-51 d is a Neptune-like planet orbiting Kepler-51, a yellow-white F-type star 2.56 thousand light-years from Earth. It is about 0.87 times the size of Jupiter and holds 0.024 Jupiter masses. It completes an orbit every 130 days at 0.51 AU from its star.
Its equilibrium temperature is about 381 K (108 °C): too cold 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: 4 spectroscopic observations, 1 of them with the James Webb Space Telescope.
It was discovered in 2014 by transit with Kepler. A planet crosses its star and dims it by a tiny, periodic fraction. Kepler-51 has 4 known planets; the others are Kepler-51 b, Kepler-51 c and Kepler-51 e.