About this world
TOI-6478 b is a Neptune-like planet orbiting TOI-6478, a cool red dwarf (type M4.0+/-) 126 light-years from Earth. It is about 4.6 times the size of Earth. It completes an orbit every 34 days at 0.11 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 204 K (−69 °C): too cold 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.