About this world
HD 199509 b is a Neptune-like planet orbiting HD 199509, a yellow, Sun-like star (type G3V) 79.3 light-years from Earth. It is about 0.66 times the size of Jupiter (its size estimated from its mass), with at least 0.14 Jupiter masses (a minimum, measured by radial velocity). It completes an orbit every 99.6 days at 0.43 AU from its star, on a strongly elongated orbit (e = 0.37).
Its equilibrium temperature is about 411 K (138 °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 2022 by radial velocity with Multiple Observatories. The star wobbles toward and away from us, Doppler-shifting its spectrum.