= Hot-Jupiter radius inflation
<Hot-Jupiter radius inflation> is the unexpectedly large <radius> of some strongly irradiated giant <exoplanets> compared with ordinary cooling and contraction models at the inferred age. A giant <planet> loses internal energy through its <exoplanet atmosphere>; slowing that loss or depositing additional energy sufficiently deep can keep its interior hotter and more extended.
Atmospheric <opacity> and <day-night heat redistribution> affect the boundary condition seen by the interior. Analytic irradiated-atmosphere work shows why deep temperatures depend on global transport as well as incident power, while also illustrating the difficulty of explaining observed radii by simple opacity changes alone.<On the radiative equilibrium of irradiated planetary atmospheres by Tristan Guillot>[Abstract: deep atmospheric temperatures, cooling/contraction and the inflated radius of HD 209458 b]{ref} An expanded <radius> is thus a constraint on the thermal history, rather than direct evidence for one unique heating mechanism.
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