About this world
TOI-178 g is a sub-Neptune orbiting TOI-178, an orange dwarf (type K) 204 light-years from Earth. It is about 2.9 times the size of Earth and holds 4.4 Earth masses. It completes an orbit every 20.7 days at 0.13 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 470 K (197 °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 2021 by transit with Transiting Exoplanet Survey Satellite (TESS). A planet crosses its star and dims it by a tiny, periodic fraction. TOI-178 has 6 known planets; the others are TOI-178 b, TOI-178 c, TOI-178 d, TOI-178 e and TOI-178 f.