About this world
HAT-P-18 b is a gas giant orbiting HAT-P-18, an orange dwarf (type K2) 526 light-years from Earth. It is about 0.95 times the size of Jupiter and holds 0.17 Jupiter masses. It completes an orbit every 5.51 days at 0.056 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 841 K (568 °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: 10 spectroscopic observations, 3 of them with the James Webb Space Telescope.
It was discovered in 2010 by transit with HATNet. A planet crosses its star and dims it by a tiny, periodic fraction.