About this world
HD 216520 b is a sub-Neptune orbiting HD 216520, an orange dwarf (type K2) 63.8 light-years from Earth. It is about 3.2 times the size of Earth (its size estimated from its mass), with at least 10 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 35.5 days at 0.2 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 482 K (209 °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 2020 by radial velocity with Multiple Observatories. The star wobbles toward and away from us, Doppler-shifting its spectrum. HD 216520 has 2 known planets; the others are HD 216520 c.