About this world
TOI-5398 c is a sub-Neptune orbiting TOI-5398, a yellow, Sun-like star (type GV) 427 light-years from Earth. It is about 3.5 times the size of Earth and holds 12 Earth masses. It completes an orbit every 4.77 days at 0.057 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 1,242 K (969 °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 2023 by transit with Transiting Exoplanet Survey Satellite (TESS). A planet crosses its star and dims it by a tiny, periodic fraction. TOI-5398 has 2 known planets; the others are TOI-5398 b.