About this world
HD 191939 c is a sub-Neptune orbiting HD 191939, a yellow, Sun-like star (type G9V) 175 light-years from Earth. It is about 3.2 times the size of Earth and holds 8 Earth masses. It completes an orbit every 28.6 days at 0.18 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 600 K (327 °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 transit with Transiting Exoplanet Survey Satellite (TESS). A planet crosses its star and dims it by a tiny, periodic fraction. HD 191939 has 6 known planets; the others are HD 191939 b, HD 191939 d, HD 191939 e, HD 191939 g and HD 191939 f.