About this world
GJ 436 b is a Neptune-like planet orbiting GJ 436, a cool red dwarf (type M2.5V) 31.8 light-years from Earth. It is about 4.2 times the size of Earth and holds 22 Earth masses. It completes an orbit every 2.64 days at 0.029 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 686 K (413 °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: 12 spectroscopic observations, 10 of them with the James Webb Space Telescope.
It was discovered in 2004 by radial velocity with W. M. Keck Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum.