Origin of olivine particles in comets

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(1)The optical constants of olivine particles were measure in the wavelengths from 7 mum to 200 mum(Mukai and Koike 1990, Icarus 87, 180). These results have confirmed the hypothesis that olivine is a carrier of a twin-peaked structure in the 10 mum region observed in several-comets.(2)Olivine particles, in general, are condenced at high temperatures(>1500 K). One possibility to explain the coexistence of olivine with icy particles inside the cometary nucleus is a radial transportation of particles near the sun to the region where the comet will be formed. We have examined the radiation pressure forces on porous aggragates to study a motion of olivine fluffy particles(Mukai et al. 1992, Astron. Astrophys. in press). It is found a significant difference of radiation forces on fluffy particles compared with those on compact spheres.(3)We have shown(Mukai 1991, IAU Col. 126, Kluwer, p. 371)that a fragmentation of fluffy dust particles due to electrostatic forces caused by electric charges on irregularly shaped particle plays an important role in the production of very small particles detected in the cometary coma of Comet P/Halley.(4)It is found(Mukai and Mukai 1990, Icarus 86, 257, Mukai et al. 1991, IAU Col. 126, Kluwer, p. 249)that these dust modelsfor fluffy aggregates can explain the photopolarimetric data observed in comets.