Possible nature of cometary atmosphere particles

Evidence is adduced for the presence of large, irregular particles in cometary atmospheres from theoretical calculations, laboratory simulations, and polarimetric and spectrophotometric observations, while attempting to more precisely define the particle parameters. It is noted that the small phase angle observation of some comets is interpretable in terms of light scattering on large, icy grains. Laboratory experiment results obtained at low temperatures and pressures may be able to explain the formation of a large, icy grain cloud near the cometary nucleus. 35 references