About this world
TOI-3984 A b is a Neptune-like planet orbiting TOI-3984 A, a cool red dwarf (type M4+/-0.) 355 light-years from Earth. It is about 0.7 times the size of Jupiter and holds 0.14 Jupiter masses. It completes an orbit every 4.35 days at 0.041 AU from its star, closer than Mercury is to the Sun, on a strongly elongated orbit (e = 0.23).
Its equilibrium temperature is about 563 K (290 °C): far too hot for liquid water on its surface. At its size it almost certainly keeps a deep envelope of hydrogen and helium. Its atmosphere has already been studied: 3 spectroscopic observations, all of them with the James Webb Space Telescope.
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.