About this world
TOI-257 b is a Neptune-like planet orbiting TOI-257, a yellow-white F-type star 251 light-years from Earth. It is about 0.64 times the size of Jupiter and holds 0.14 Jupiter masses. It completes an orbit every 18.4 days at 0.15 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 1,027 K (754 °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.