The Ultraviolet Irradiated Ionosphere of Hot Jupiter KELT-20b
Orbiting an A-type primary star, the exoplanet KELT-20b , also designated MASCARA-2b , stands as a prime example of the extreme thermal environments characteristic of ultra-hot Jupiters . Unlike planets residing within the cooler zones of their host systems, KELT-20b experiences intense irradiation due to its proximity to a star significantly hotter and more luminous than the Sun. The resulting atmospheric conditions are governed by extreme thermal forcing , which drives the chemical and physical processes defining this gaseous titan. The physical composition of KELT-20b is dominated by hydrogen and helium, yet its high equilibrium temperature permits the existence of a unique chemical state in its upper atmosphere. At these altitudes, the presence of metal species such as iron and vaporized chromium has been confirmed through transit spectroscopy . These materials exist in a g...