Modeling of mid-infrared dust emission from P\Swift-Tuttle

Comet P\Swift-Tuttle was observed at 11.7 μm on 12 nights over the course of three weeks in November 1992 using the UCSD mid-infrared imaging camera (Fomenkova et al., 1995). The large number of images obtained and the overall high quality of the data permit the continued study of the rich dust structures apparent in this active comet. We present a model to interpret the features observed in these images using olivine spheres (MgFeSiO4) as representative dust grains, and illustrate the validity of the model by applying it to the image taken on UT 9.1 November. A fully three-dimensional Monte Carlo simulation based on the Finson–Probstein model (Fomenkova et al., 1995) is performed, and Mie scattering theory is used to characterize the properties of the grains. We found that the comet executes simple rotation about an axis whose obliquity is 45±10°. Our best-fit dust grain size distribution in the size range from 0.6 to 10.0 μm is of the form f (a) ∼ a−β with β = 2.5±0.5, not quite as steep as the distribution (β = 3.7) measured for comet P\Halley (McDonnell et al., 1991).