The infrared emission of various comets can be matched within the framework that all comets are made of aggregated interstellar dust. This is demonstrated by comparing results on Halley (a periodic comet), Borrelly (a Jupiter family short period comet), Hale-Bopp (a long period comet), and extra-solar comets in the beta Pictoris disk.
It has been shown that the simultaneously observed properties for Halley such as chemical composition, size (mass) distribution, infrared emission are consistent with the comet dust model as very fluffy aggregates of submicron interstellar silicate core-organic refractory mantle particles.
We have calculated the thermal emission spectrum of the dust of comet P/Borrelly (1987 XXXIII), a Jupiter family short-period comet, from 3 mum to 14 mum as well as the 10 mum silicate feature. The fluffy aggregate model of silicate core-amorphous carbon mantle grains with a porosity P=0.85 can match the observational data quite well. It seems that, compared to the Halley dust, the dust grains of P/Borrelly appear to be relatively more processed (more carbonized), less fluffy, and richer in smaller particles. A statistical analysis of fifteen comets indeed seems to suggest that the dust size distribution is somewhat steeper for short-period comets than for long-period comets.
We have proposed a comet dust model for the beta Pictoris disk assuming the dust in the disk plane is continually replenished by comets orbiting the star where the dust is quickly swept out by radiation pressure or spiral onto the star as a result of Poynting-Robertson drag. The fluffy aggregate comet dust model provides a good match to the 10 mum amorphous and the 11.2 mum crystalline silicate spectral emission as well as the excess continuum flux from the disk over a wide range of wavelengths.
We have also modeled the 3-20 mum IR thermal emission spectrum of comet Hale-Bopp (C/1995 O1) at a heliocentric distance of rh=1.15 AU. Good fits have been obtained in terms of the comet dust model as fluffy aggregates of interstellar dust. Our results are significantly different from the common thought that Hale-Bopp is rich in submicron grains. The mean grain masses derived here are two to three orders of magnitude higher than those estimated from the empirical superheat method or from the IR emission modeling both of which use compact silicate/carbon particles.