However, as an EGP of whatever mass cools, its atmospheric composition evolves through a similar chemical and condensation sequence. Figure 1 depicts the atmospheric temperature/pressure (T/P) profile for a sequence of 1-, 5-Gyr models as a function of orbital distance from a G2V star. As the planet “moves" outward, its atmospheric temperature at a given pressure decreases. Superposed on the plot are the H$_2$O and NH$_3$ condensation lines. In an approximate sense, a given atmospheric composition and temperature can result from many combinations of orbital distance, planet mass, stellar type, and age. This lends an added degree of complexity to the study of EGPs with which the study of stars does not need to wrestle.

The atmospheres of close-in EGPs (“roasters") at orbital distances of $\sim$0.02-0.07 AU from a G, F, or K star are heated and maintained at temperatures of 1000-2000 K, roughly independent of planet mass or composition. An edge star of the solar-composition, hydrogen-burning main sequence ($\sim$75 ) has a  of $\sim$1700 K. Therefore, an irradiated EGP, with a radius comparable to that of such a star, can be as luminous. Its atmospheric composition is predominantly H$_2$, He, H$_2$O, Na, K, and CO. At high temperatures, carbon 