About this world
HD 209458 b is a gas giant orbiting HD 209458, a yellow, Sun-like star (type G0V) 158 light-years from Earth. It is about 1.4 times the size of Jupiter and holds 0.73 Jupiter masses. It completes an orbit every 3.52 days at 0.047 AU from its star, closer than Mercury is to the Sun.
Its equilibrium temperature is about 1,459 K (1,186 °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: 48 spectroscopic observations, 5 of them with the James Webb Space Telescope.
It was discovered in 1999 by radial velocity with W. M. Keck Observatory. The star wobbles toward and away from us, Doppler-shifting its spectrum.