Optical properties of fluffy aggregates as analogue of interplanetary dust particles

Based on the appearance of chondritic porous aggregates collected from stratosphere, we have modeled interplanetary dust particles as fluffy aggregates consisting of submicron-sized spherical monomers. The optical properties are calculated by a modified version of the discrete dipole approximation where the dipole polarizability is determined by the first term of scattering coefficient in the Mie theory. The accuracy of our calculations is confirmed through the comparison with the rigorous solutions for cluster of spherical monomers. It is found that fluffy aggregates have larger cross sections and less resonant structures in the scattering profiles in comparison with the volume-equivalent sphere. Our model results in consistent behaviors with the observation of zodiacal light, i.e., slow rise towards the backward direction and negative polarization between the scattering angles 160° ≤ θ ≤ 180°. For two sets of optical constants of dielectric materials, these properties are not sensitive to the size of an aggregate as long as the monomer size is smaller than the incident wavelength.