Modeling of the light scattering properties of cometary dust using fractal aggregates

Aims: The nature of cometary dust is still elusive. In order to constrain the physical properties of dust in cometary coma, we modeled the observed scattering parameters, investigating different morphological and compositional effects. Methods: We used fractal aggregates as dust particles. The scattering behavior of extremely elongated dust particles, similar to those formed in micro-gravity aggregation experiments and more compact aggregates, have been studied with the discrete-dipole approximation theory. Results: Results show that particles comparable in size to the incident wavelength provide the best qualitative fits. A silicate composition gives a good fit to the polarization and the phase function, but is characterized by large albedo. Organic and mixed compositions provide low albedos but do not fit the polarization and phase function curves well. Compact particles seem to reproduce the observed parameters better, indicating a possible morphological metamorphism of dust since the time of formation. The observed different polarization classes may be explained in terms of different monomer sizes, if a cluster of spheres models are used. © ESO 2006.