Exoplanet Chemistry

The terrestrial and gas-giant planets in our solar system may represent some prototypes for planets around other stars; the exoplanets because most stars have similar overall elemental abundances as our sun. The solar system planets represent at least four chemical planet types, depending on the phases that make them: Terrestrial-like planets made of rock (metal plus silicates), Plutonian planets made of rock and ice, Neptunian giant planets of rocky, icy with low H and He contents, and Jovian gas-giant planets of rocky, icy planets with near-solar H and He contents. The planetary compositions are linked to the chemical fractionation in the planetary accretion disks. Chemical tracers of these fractionations are described. Many known exoplanets are gas-giant planets with up to several Jupiter-masses and their atmospheric chemistry is compared to that of brown dwarfs. Exoplanets in close orbits around their host stars may resemble hot brown dwarfs (L-dwarfs). Planets receiving less radiation form their host may compare more to the methane-rich T dwarfs. The cloud layers resulting from condensation of oxides, metal, sulfides, and salts in these hot and cool gas giant planets and their chemical tracers are described.