About this world
HD 5278 b is a sub-Neptune orbiting HD 5278, a yellow-white F-type star (type FV) 188 light-years from Earth. It is about 2.5 times the size of Earth and holds 7.8 Earth masses. It completes an orbit every 14.3 days at 0.12 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 943 K (670 °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 transit with Transiting Exoplanet Survey Satellite (TESS). A planet crosses its star and dims it by a tiny, periodic fraction. HD 5278 has 2 known planets; the others are HD 5278 c.