Reconciling main belt asteroid spectral flux density measurements with a self-consistent thermophysical model

Thermophysical models consistent with Earth’s Moon and infrared and submillimeter measurements obtained during the Rosetta fly-by of Asteroid (21) Lutetia have been applied to computations of thermal fluxes from Asteroids (4) Vesta, (1) Ceres, (2) Pallas, and (10) Hygiea. Comparisons are made with Earth- and space-based flux measurements that cover the infrared-to-centimeter wavelength spectrum. The models account for diurnal and seasonal effects as well as viewing geometry at the epochs of the observational data. Model fluxes at submillimeter and longer wavelengths are computed from a radiative transfer integral that takes into account temperature gradients in the subsurface and a plausible range of lunar-like electrical properties. A surface roughness model in the form of hemispherical mini-craters is included in the evaluation of the infrared flux comparisons. s of the infrared-to-centimeter comparisons confirm that low thermal inertia (I ∼ 5–80 J/(K m2 s0.5)) material constitutes the upper ∼1 cm of the four large asteroids studied. For the non-isothermal models considered, spectral emissivities near 1.0 fit the data of all four asteroids with no significant variations indicated throughout the infrared to microwave spectrum. Enhanced measured infrared flux levels (relative to a smooth surface model) of the four asteroids are constrained by a surface model with up to 50% fractional coverage of hemispherical craters, consistent with both the recent Lutetia result and historical measurements of the Moon’s thermal flux characteristics.