Albedo and Diameter Distributions of Asteroid Families Using the Spitzer Asteroid Catalog

The Spitzer Asteroid Catalog contains flux measurements of asteroidsserendipitously observed in publicly available Spitzer data. At present,this catalog contains some 10,000 measurements at 24 microns only, andwill ultimately contain 100,000 measurements or more. These measurements, along with with optical photometry from the the MinorPlanet Center, are used to calculate the albedos and diameters of asteroids using the Standard Thermal Model (Lebofsky et al 1986) and theNear Earth Asteroid Thermal Model (Harris 1998). In this study we used these data to investigate the albedo and diameter distributions with inasteroid families. Asteroid families are groups of asteroids with similar orbital properties that are thought to be fragments of pastasteroid collisions. Around one third of known asteroids are members ofasteroid families. For the first time, the homogeneity of albedos with inasteroid families can be measured. Additionally, true diameters can be used to study size distributions within asteroid families. We used the Hierarchical Clustering Method of Zappala et al (1995) to identify family members. We will present results from our study, including meanand dispersion of albedos for a number of inner and outer main belt asteroid families of different ages. We will also present sizedistributions for these asteroid families. We will discuss the implications for the history of these asteroid families and, by extension, the main asteroid belt. This work is based in part on archival data obtained with the Spitzer Space Telescope, which isoperated by the Jet Propulsion Laboratory, California Institute ofTechnology under a contract with NASA. Support for this work was provided by an award issued by JPL/Caltech