부산대학교 도서관

We investigate the physical characteristics of the Solar System's proposedPlanet Nine using modeling tools with a heritage in studying Uranus andNeptune. For a range of plausible masses and interior structures, we find upperlimits on the intrinsic Teff, from ~35-50 K for masses of 5-20 M_Earth, and wealso explore lower Teff values. Possible planetary radii could readily spanfrom 3 to 6 R_Earth depending on the mass fraction of any H/He envelope. Givenits cold temperature, the planet encounters significant methane condensation,which dramatically alters the atmosphere away from simple Neptune-likeexpectations. We find the atmosphere is strongly depleted in molecularabsorption at visible wavelengths, suggesting a Rayleigh scattering atmospherewith a high geometric albedo approaching 0.75. We highlight two diagnostics forthe atmosphere's temperature structure, the first being the value of themethane mixing ratio above the methane cloud. The second is the wavelength atwhich cloud scattering can be seen, which yields the cloud-top pressure.Surface reflection may be seen if the atmosphere is thin. Due tocollision-induced opacity of H2 in the infrared, the planet would be extremelyblue (instead of red) in the shortest wavelength WISE colors if methane isdepleted, and would, in some cases, exist on the verge of detectability byWISE. For a range of models, thermal fluxes from ~3-5 microns are ~20 orders ofmagnitude larger than blackbody expectations. We report a search of the AllWISESource Catalog for Planet Nine, but find no detection.