Albedo and Reflection Spectra of Extrasolar Giant Planets

We generate theoretical albedo and reflection spectra for a full range ofextrasolar giant planet (EGP) models, from Jovian to 51-Pegasi class objects.Our albedo modeling utilizes the latest atomic and molecular cross sections, aMie theory treatment of extinction by condensates, a variety of particle sizedistributions, and an extension of the Feautrier radiative transfer methodwhich allows for a general treatment of the scattering phase function. We findthat due to qualitative similarities in the compositions and spectra of objectswithin each of five broad effective temperature ranges, it is natural toestablish five representative EGP albedo classes: a ``Jovian'' class (T$_{\rmeff} \lesssim 150$ K; Class I) with tropospheric ammonia clouds, a ``watercloud'' class (T$_{\rm eff} \sim 250$ K; Class II) primarily affected bycondensed H$_2$O, a ``clear'' class (T$_{\rm eff} \gtrsim 350$ K; Class III)which lacks clouds, and two high-temperature classes: Class IV (900 K$\lesssim$ T$_{\rm{eff}}$ $\lesssim$ 1500 K) for which alkali metal absorptionpredominates, and Class V (T$_{\rm{eff}}$ $\gtrsim$ 1500 K and/or low surfacegravity ($\lesssim$ 10$^3$ cm s$^{-2}$)) for which a high silicate layershields a significant fraction of the incident radiation from alkali metal andmolecular absorption. The resonance lines of sodium and potassium are expectedto be salient features in the reflection spectra of Class III, IV, and Vobjects. We derive Bond albedos and effective temperatures for the full set ofknown EGPs and explore the possible effects of non-equilibrium condensedproducts of photolysis above or within principal cloud decks. As in Jupiter,such species can lower the UV/blue albedo substantially, even if present inrelatively small mixing ratios.