About this world
HD 28109 c is a Neptune-like planet orbiting HD 28109, a yellow-white F-type star (type F8) 455 light-years from Earth. It is about 4.1 times the size of Earth and holds 9.2 Earth masses. It completes an orbit every 56 days at 0.31 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 643 K (370 °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 transit with Transiting Exoplanet Survey Satellite (TESS). A planet crosses its star and dims it by a tiny, periodic fraction. HD 28109 has 3 known planets; the others are HD 28109 b and HD 28109 d.