Light Scattering as a Diagnostic for Asteroid Structure

With the identification of the Veritas family as the source of the 9.35 degree dust band of the Zodiacal cloud (Nesvory, et. al 2003), instead of the formerly assigned Eos, we are presented with a new means to study the Veritas family and its precursor asteroid. When an asteroid breaks up, the larger pieces remain together on the same orbit and may reassemble into what is known as a rubble pile. The smaller (sub-millimeter to micron sized) particles, however, experience a stronger perturbation from the solar radiation pressure and these particles migrate to the zodiacal cloud, rather than remaining with the rubble pile. The light scattering of this corresponding band of the zodiacal cloud can be studied for information on the dust particles comprising it, specifically their size and structure, and thus also their precursor asteroid. Using the unique capability of the Microwave Scattering Facility (Gustafson 1996), models of these dust particles are created and the scattering by these particles is measured, specifically the intensities and polarizations. The models are based on the currently known data for the Veritas family, i.e. taxonomic class, tensile strength(calculated from light curves), break-up epochs (obtained from theoretical orbital integrations), and albedo dispersion. Our current hypothesis is that the Veritas precursor was NOT differentiated, but rather it was an aggregate of interstellar grains like the Bird's Nest model of dust proposed by Greenberg and Gustafson(1981). The Bird's Nest model represents the dust as pieces of aggregated nebular dust from which water ice has sublimated. We expect to find structure in the zodiacal dust on the scale of the size of the interstellar grains, 0.1-0.7 microns. If, however, the precursor WAS differentiated then the bulk material in the dust should appear homogeneous (for full differentiation) or show struucture on a different size scale (for partial differentiation). We present here our method and first results.