The thermal emission of Kuiper Belt objects

A thermophysical model, previously used to compute the surface tempeature distribution of spherical asteroids taking into account thermal inertia and rotational characteristics, has been developed to incorproate tri-axial ellipsoidal geometry and arbitrary spin axis orientation. The numerical model has been used to predict the thermal IR fluxes from Kuiper Belt objects (KBOs), particularly at wavelengths at which detection by the ISOPHOT instrument on ISO appears feasible. The dependence of the fluxes on the magnitude of a thermal parameter, the orientation of the spin axis, and the ratio of the major and minor axes are described for an assumed prolate ellipsoid. Comparisons with ground-based observation of 2060 Chiron are made showing that values of the thermal parameter less than I can be reconciled with the data. The effects of sublimation have been incorporated into the model and it is shown that sublimation of CO₂ ice KBOs will have little effect on the surface temperature while out-gassing rates in excess: of 10¹⁶ molecule m^-2δ^-1 are possible.