About this world
HD 20781 d is a sub-Neptune orbiting HD 20781, an orange dwarf (type K0V) 117 light-years from Earth. It is about 3.3 times the size of Earth (its size estimated from its mass), with at least 11 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 29.2 days at 0.16 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 570 K (297 °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 2019 by radial velocity with La Silla Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum. HD 20781 has 4 known planets; the others are HD 20781 b, HD 20781 c and HD 20781 e.