About this world
GJ 876 d is a sub-Neptune orbiting GJ 876, a cool red dwarf (type M2.5V) 15.2 light-years from Earth. It is about 2.5 times the size of Earth (its size estimated from its mass) and holds 6.8 Earth masses. It completes an orbit every 1.94 days at 0.021 AU from its star, closer than Mercury is to the Sun, on a strongly elongated orbit (e = 0.21).
Its equilibrium temperature is about 603 K (330 °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 2005 by radial velocity with W. M. Keck Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum. GJ 876 has 4 known planets; the others are GJ 876 c, GJ 876 b and GJ 876 e.