A significant advance in the knowledge of exoplanet interiors and atmospheres has been made possible with the discovery of transiting exoplanets. Densities from their masses and radii are providing the first indications of their interior structure and composition, while broadband brightness temperature measurements from transit photometry and spectroscopy are providing the first insights into their atmospheric composition and thermal transport processes. All of this has been substantially facilitated by the knowledge of interiors and irradiated atmospheres of solar system planets and satellites acquired over the last half century.
Physical models of exoplanets span two extreme classes of object, and potentially much in between: the low-mass high-density ‘solid’ planets dominated by metallic cores and silicate-rich and/or ice-rich mantles, and the high-mass low-density gas giants dominated by their massive accreted H/He envelopes.
For the gas-rich giants, models of their interiors and models of their atmospheres are closely connected, and the most recent atmospheric models couple their emergent flux with their assembly by core accretion. Models of their interiors predict bulk properties such as the pressure-temperature relation, and their radii as a function of mass. For close-in, highly irradiated gas giants, the additional external heat source has a significant effect on the pressure–temperature structure of the outer atmosphere. Combined with inferences on their probable bulk chemical composition, atmospheric models also predict broad-band colours and spectral features arising from specific atomic and molecular species.