About this world
GJ 229 A c is a sub-Neptune orbiting GJ 229, a cool red dwarf (type M1.5V) 18.8 light-years from Earth. It is about 2.9 times the size of Earth (its size estimated from its mass), with at least 8.6 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 122 days at 0.38 AU from its star, closer than Mercury is to the Sun, on a strongly elongated orbit (e = 0.37).
Its equilibrium temperature is about 188 K (−85 °C): too cold for liquid water on its surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium.
It was discovered in 2020 by radial velocity with Multiple Facilities. The star wobbles toward and away from us, Doppler-shifting its spectrum. GJ 229 has 2 known planets; the others are GJ 229 b.