Scattering properties and composition of cometary dust
  Composition of Comet dust obtained by the dust impact analyser on the Halley probes indicated that the comet dust is a mixure of silicate and carbonaceous material. The collected interplanetary dust particles (IDP's) are fluffy and composite having grains of several different types stuck together. Using Discrete Dipole Approximation (DDA) we study the scattering properties of composite grains. In particular, we study the angular distribution of the scattered intensity and linear polarization of composite grains. We assume that the composite grains are made up of host silicate sphere/spheroid with the inclusions of graphite. Results of our calculations on the composite grains show that the angle of maximum polarization shifts, and the degree of polarizaion varies with the volume fraction of inclusions. We use these results on the composite grains to interpret the observed scattering in the cometary dust. 
Ranjan Gupta, D.B. Vaidya, J.S. Dobbie and P. Chylek