  There are now many known exoplanets with Msin(i) within a factor of two of
Neptune's, including the transiting planets GJ436b and HAT-P-11b. Planets in
this mass-range are different from their more massive cousins in several ways
that are relevant to their radiative properties and thermal structures. By
analogy with Neptune and Uranus, they are likely to have metal abundances that
are an order of magnitude or more greater than those of larger, more massive
planets. This increases their opacity, decreases Rayleigh scattering, and
changes their equation of state. Furthermore, their smaller radii mean that
fluxes from these planets are roughly an order of magnitude lower than those of
otherwise identical gas giant planets. Here, we compute a range of plausible
radiative equilibrium models of GJ436b and HAT-P-11b. In addition, we explore
the dependence of generic Neptune-mass planets on a range of physical
properties, including their distance from their host stars, their metallicity,
the spectral type of their stars, the redistribution of heat in their
atmospheres, and the possible presence of additional optical opacity in their
upper atmospheres.
