About this world
HD 5278 c is a Neptune-like planet orbiting HD 5278, a yellow-white F-type star (type FV) 188 light-years from Earth. It is about 4.5 times the size of Earth (its size estimated from its mass), with at least 18 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 40.9 days at 0.24 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 665 K (392 °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 2021 by radial velocity with Paranal Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum. HD 5278 has 2 known planets; the others are HD 5278 b.