About this world
HD 18599 b is a sub-Neptune orbiting HD 18599, an orange dwarf (type K2V) 126 light-years from Earth. It is about 2.6 times the size of Earth and holds 24 Earth masses. It completes an orbit every 4.14 days at 0.048 AU from its star, closer than Mercury is to the Sun, on a strongly elongated orbit (e = 0.34).
Its equilibrium temperature is about 863 K (590 °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.