A Comparison of Autoclass and Principal Component Analysis as Applied to Asteroid Families

Document Type

Conference Proceeding

Publication Date


Publication Title

American Astronomical Society, Department of Planetary Sciences


We present and compare the Sloan Digital Sky Survey (SDSS) colors of the Themis family, an older (2.5 Gya) outer-belt asteroid family, with that of the Beagle family (15 Mya), Themiss younger second-generation family. Comparing Beagle family colors with that of its older progenitor's family's colors allows a direct test of space weathering effects on C-complex asteroids. The question of space weathering among CComplex asteroids is an unsettled one. Nesvorny et al[1] found clear color differences between C-complex asteroids of different ages, which could be explained by space weathering processes. The trend with age that they determined based upon Principal Component Analysis (PCA) was anchored with the older Themis family at one extreme. Critical to the weathering hypothesis is the assumption that these asteroids would have similar un-weathered compositions. The catastrophic disruption of the Beagle family eliminates this question since its composition is that of its progenitor Themis member. The size of the SDSS dataset allows us to analyze these families using two statistical methods, PCA and Autoclass. Combined, these powerful methods provide a detailed picture of the role of space weathering among these asteroids