  Here we show preliminary calculations of the cooling and contraction of a 2
MJ planet. These calculations, which are being extended to 1-10 MJ, differ from
other published "cooling tracks" in that they include a core accretion-gas
capture formation scenario, the leading theory for the formation of gas giant
planets. We find that the initial post-accretionary intrinsic luminosity of the
planet is ~3 times less than previously published models which use arbitrary
initial conditions. These differences last a few tens of millions of years.
Young giant planets are intrinsically fainter than has been previously
appreciated. We also discuss how uncertainties in atmospheric chemistry and the
duration of the formation time of giant planets lead to challenges in deriving
planetary physical properties from comparison with tabulated model values.
