Interactions with Electromagnetic Radiation: Theory and Laboratory Simulations
At the time of the most recent major book on interplanetary dust (McDonnell 1978), most theoretical studies were confined to homogeneous and spherical dust models. Only microwave analogue experiments were used to explore the scattering by more realistic s
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University of Florida, Gainesville, Florida, USA Leiden University, Leiden, Netherlands Jena-Optronik GmbH, Jena, Germany
Abstract. At the time of the most recent major book on interplanetary dust (McDonnell 1978), most theoretical studies were confined to homogeneous and spherical dust models. Only microwave analogue experiments were used to explore the scattering by more realistic structures representing either the first stratospheric collections of interplanetary dust particles or complex aggregates of interstellar grains proposed on theoretical grounds. Advances in computing power, light scattering theory, and in experimental capabilities have since allowed the implementation of powerful and flexible theoretical solutions, more sophisticated solutions for the calculation of scattering by interacting particles based on classical methods, and have led to multi-wavelength microwave analogue investigations of structures in the size range of interplanetary dust. We attempt to summarize these advances, place them into context, and suggest a framework for models of interplanetary dust that facilitates systematic studies. The electromagnetic scattering sections apply to a broad range of natural and artificial terrestrial and cosmic dust or aerosols as well as to interplanetary dust.
I. INTRODUCTION Studies described in this book point to a complex interplanetary dust system where fragments from comets and asteroids are believed to dominate over impact ejecta and volcanic cinders originating from planetary satellites. These dust populations mix with smaller amounts of ejectae from planetary surfaces and with interstellar grains that are now also known to permeate interplanetary space. Modern grain models are based on a combination of properties derived from in-situ and remote measurements, collected samples, theoretical and laboratory models all of which are plagued by uncertainties and biases. There is however no doubt that they reveal that at least some of the particles are aggregates. The realization that we are not faced with dust of a single and simple morphology but a range in particle properties including some highly complex structures has become widely accepted only gradually. At the time of the most recent major book on interplanetary dust (McDonnell 1978), most works on light scattering by interplanetary dust were still based on a homogeneous grain material with a spherical boundary. The "frontier" of light scattering research was for the most E. Grün et al. (eds.), Interplanetary Dust © Springer-Verlag Berlin Heidelberg 2001
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part in exploration of the effects of non-spherical particle shapes. While some groups also worked on the development of theoretical solutions for scattering by porous or aggregate particle structures, only microwave analogue experiments were used to explore the scattering by "Fluffy" structures representing the first stratospheric collections (Giese et al. 1978) and complex "Bird's-Nest" aggregates of interstellar grains proposed on theoretical
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