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Published online by Cambridge University Press: 27 February 2018
Halley probes (Giotto, Vega) have shown that cometary grains can be extremely dark and might have fluffy structures. These probes have also detected submicron sized particles in the coma of the comet. In view of these observations and to interpret the observed data on several other comets we calculate the angular distribution of the scattered intensity, polarization and albedo for porous and compact particles. For these calculations, we apply discrete dipole approximation (DDA) first to the spheroidal particles, assumed to be made of small scattering elements (dipoles). Then we reduce the number of dipoles systematically to model the porous grains. We study the phase function, linear polarization, and albedo as a function of grain size and packing density.