About this world
TOI-5817 b is a sub-Neptune orbiting TOI-5817, a yellow, Sun-like star (type G2IV-V) 263 light-years from Earth. It is about 3.1 times the size of Earth and holds 10 Earth masses. It completes an orbit every 15.6 days at 0.12 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 950 K (677 °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 2025 by transit with Transiting Exoplanet Survey Satellite (TESS). A planet crosses its star and dims it by a tiny, periodic fraction.