DPS 2001 meeting, November 2001
Session 46. Cometary Atmospheres and Solar Wind Interaction
Oral, Chairs: M. Hanner, A. Levasseur-Regourd, Friday, November 30, 2001, 3:00-4:10pm, Regency E

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[46.06] Evidence for icy grains in cometary comae

D.J. Lien (Oklahoma State University)

Recent studies of cometary dust dynamics has focused primarily on interpreting the near-nuclear features seen in bright comets (rings, arcs, and spikes) in terms of of a combination of surface activity, ejection speed, grain properties (\beta = ratio of radiation pressure to gravity) and projection effects. Simple dynamical models have been developed which reproduce most of the observed features in the inner coma. Unfortunately, when extended to larger image scales, these models do not match the nearly featureless dust coma and tail, nor are they successful in predicting the shape or distinct sunward edge of the parabolic head of the dust coma. Numerical simulations of C/Hyakutake and C/Hale-Bopp will be presented which illustrate this problem. A preliminary solution will be presented where the arcs and rings are created by particles emitted from the surface with a small range of velocities independent of \beta and the outer, featureless dust coma (including the parabolic head) is created by the fragmentation or sublimation of these original particles. This secondary source of dust is dispersed randomly with speeds which vary as v \propto \sqrt{\beta}. An argument will be presented which suggests that the material ejected from the nucleus is composed primarily of ices, which then sublimate, releasing embedded dust. It is this secondary source of dust which is detected at visible and IR wavelengths.

The author(s) of this abstract have provided an email address for comments about the abstract: liend@okstate.edu

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