About this world
HD 158259 c is a sub-Neptune orbiting HD 158259, a yellow, Sun-like star (type G0) 88.2 light-years from Earth. It is about 2.2 times the size of Earth (its size estimated from its mass), with at least 5.6 Earth masses (a minimum, measured by radial velocity). It completes an orbit every 3.43 days at 0.046 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 1,473 K (1,200 °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 Haute-Provence Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum. HD 158259 has 5 known planets; the others are HD 158259 b, HD 158259 d, HD 158259 e and HD 158259 f.