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J. Lasue, A.C. Levasseur-Regourd (Université Paris 6, Service d'Aéronomie)
Most of the available data regarding cometary dust physical properties stem from the observations of the light scattered by dust comae. The polarization observations show smooth phase curves and a quasi-linear increase of the polarization with the wavelength for phase angles in the 30° to 50° range [1,2]. Recently, the Stardust mission has probed the coma of comet Wild 2, and found that the large dust particles could be open structures of sub-micrometer silicate or organic components [3].
We present numerical simulations of light scattering by fractal aggregates (formed by ballistic cluster-cluster (BCC) or by ballistic particle-cluster (BPC) aggregation) of sub-micron sized grains. Calculations are presented for aggregates of 64 grains and more, either homogeneous (silicate or organics), or core-mantle(s) grains with a silicate core and layers of organics or volatile components. Phase angle and wavelength dependence of the polarization (and brightness) are presented. We show that BCC aggregates of core-mantle grains, a fair approximation of the agglomeration of grains of interstellar origin in the early Solar System, reasonably simulate characteristic trends in photometric and polarimetric observations.
Support from ESA is acknowledged
[1] Hanner, JQSRT 79-80, p695-705, 2003. [2] Levasseur-Regourd et al., JQSRT 79-80, p903-10, 2003. [3] Tuzzolino et al., Science 304, no 5678, p1776-80, 2004.
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Bulletin of the American Astronomical Society, 36 #4
© 2004. The American Astronomical Soceity.