Michael Kelley, Ph.D. 2006

Ph.D Thesis

The Size, Structure and Minerology of Comet Dust

by Michael Kelley

Under the supervision of Dr. Chick Woodward


Early in our solar system's history, dust in the proto-solar nebula was processed and subsequently incorporated into planets and planetesimals, such as moons, asteroids, and comets. Today, comets are one of the best preserved reservoirs of material from the epoch of planet formation. The mineralogy of comet dust may be directly linked to the mineralogy of the early outer solar system. Remote observations of a wide variety of comets are necessary to census the population of comets and their dust properties.

This dissertation is an investigation of the physical properties of comet dust through analytical and observational techniques. We are examining comet dust size, structure (e.g., shape, porosity), and mineralogy. To achieve this goal, we observed comets with multi-wavelength imaging, polarimetry, and spectroscopy, and created a program to model comet dust dynamics and simulate observations of comet comae, tails, and trails. An emphasis is placed on observations of dust thermal emission with the Spitzer Space Telescope, a space-borne, infrared telescope. Dust properties are also constrained by scattered light observations, especially polarimetry, and a complete theory of comets must describe both thermal emission properties (mid-infrared spectral energy distributions) and scattered light properties (optical/near-infrared spectral energy distributions and polarization) of comet dust. To this end, we present: near-infrared polarimetry of nine comets; a dynamic model to simulate comet dust trails and an in-depth analysis of the dust trail of comet 67P/Churyumov-Gerasimenko; a Spitzer spectroscopy survey of comet dust and an analysis of the dust properties of comets 2P/Encke, 67P/Churyumov-Gerasimenko, and C/2001 HT50 (LINEAR-NEAT); and an analysis of multi-epoch Spitzer images and near-infrared ground-based spectroscopy to assess the size distribution of dust ejected from comet 9P/Tempel~1 as a result of collision the with the Deep Impact spacecraft.