Interpreting the thermal properties of cometary dust

The characteristics of the thermal emission from cometary dust are discussed and the observations compared with models for absorbing and silicate grains. The observed JHK colors are discussed and suggested observations of future comets are outlined. The observed 4.8 microns/3.5 microns flux ratio can be fit with absorbing grains, with a variation in particle size less than a factor of 2 for all comets observed. The relative number of silicate grains necessary to produce an observable feature at 10 microns is a strong function of their temperature. If they are cold (no absorption at visual wavelengths), a considerable number could be present without producing a detectable feature above the thermal continuum from the hot absorbing grains.