Atmospheric characteristics and chemical processes of gas giant exoplanets orbiting close to their stars.Hot Jupiters are gas giant exoplanets that orbit their host stars at extremely close distances, typically less than one-tenth of the distance between Mercury and the Sun. This proximity means they are intensely irradiated, leading to atmospheric temperatures that can exceed 1000°C, and in some cases, even 3000°C. These extreme conditions drive a unique set of atmospheric processes, including the evaporation of heavy elements, the formation of mineral clouds, and the presence of exotic chemical compounds that would be unstable under cooler conditions.
The first hot Jupiter, 51 Pegasi b, was discovered in 1995 by Michel Mayor and Didier Queloz, a finding that earned them the 2019 Nobel Prize in Physics. This discovery challenged existing models of planet formation, as such massive planets were not expected so close to their stars.
The intense stellar radiation heats the planet's upper atmosphere, causing it to expand and, in some cases, escape entirely as a comet-like tail. The heat also drives strong winds that redistribute energy from the dayside to the nightside, creating dramatic temperature contrasts. In ultra-hot Jupiters, temperatures are so high that molecules like water and titanium oxide dissociate, and metals like iron and magnesium exist as gases, condensing into clouds on the cooler nightside.
Hot Jupiters serve as natural laboratories for studying atmospheric physics under extreme conditions, and their large size and short orbital periods make them prime targets for transmission spectroscopy with instruments like the James Webb Space Telescope.
Some hot Jupiters, like WASP-121b, have atmospheres so hot that they evaporate heavy metals like iron and magnesium, which then escape into space, creating a comet-like tail.





























