About this world
HIP 9618 b is a sub-Neptune orbiting HIP 9618, a yellow, Sun-like star 220 light-years from Earth. It is about 3.8 times the size of Earth and holds 8.3 Earth masses. It completes an orbit every 20.8 days at 0.14 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 641 K (368 °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: 2 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. HIP 9618 has 2 known planets; the others are HIP 9618 c.