Model of a Kuiper Belt Small Grain Population and Resulting Far-Infrared Emission

Abstract

We have calculated a simple model of the expected Kuiper Belt (KB) small grain population and the thermal emission that would arise from such grains. We have also sought observational evidence for this emission. The model assumed equilibrium between grain creation by collisional fragmentation of comets and removal by Poynting-Robertson radiation drag, radiation pressure-driven ejection, mutual collisions, and sublimation. The model far-IR intensity scales as the square of total KB mass. Comparison of our model with observations of the zodiacal dust rules out emission from trans-Neptunian dust representing more than about 0.3 M of KB comets. This agrees with recent HST reports of a population of comet-sized bodies in the KB which has a minimum mass of about 0.04 M, although that population can be extrapolated to include as much as 1 M in the volume of our model. The model KB dust fractional bolometric luminosity (L_dust/L_star) would have about 10^-2 and 10^-4 of the values for the grain disks around Vega and β Pic, respectively. A preliminary search in COBE DIRBE data reveals nonuniform bands near the ecliptic of cold (T = 20-30 K) emission prominent at wavelengths of 140 and 240 μm but not prominent relative to zodiacal emission at shorter (IRAS) wavelengths. Most of this emission is probably not from solar system material.