About this world
Kapteyn c is a sub-Neptune orbiting Kapteyn, a cool red dwarf (type M2.0V) 12.8 light-years from Earth. It is about 2.5 times the size of Earth (its size estimated from its mass), with at least 7 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 122 days at 0.31 AU from its star, closer than Mercury is to the Sun, on a strongly elongated orbit (e = 0.23).
Its equilibrium temperature is about 166 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.
It was discovered in 2014 by radial velocity with Multiple Observatories. The star wobbles toward and away from us, Doppler-shifting its spectrum.