= Atmospheric metallicity of a giant planet
The <atmospheric metallicity of a giant planet> describes its atmospheric inventory of elements heavier than <hydrogen> and <helium>. It must specify a convention: an elemental abundance ratio relative to <hydrogen>, an enhancement relative to a reference composition, or a total heavy-element <mass fraction> are related but different quantities. A quoted enrichment also needs to identify its reference, such as the host <star>.
<Atmospheric retrieval> estimates molecular abundances, which must then be connected to elemental inventories through a model of <chemical equilibrium> or <disequilibrium chemistry in an exoplanet atmosphere>. <Atmospheric condensate rainout> can hide elements in particles below the observed levels. Thus an atmospheric enrichment need not directly equal the heavy-element fraction of the whole <exoplanet interior>.
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