Reflectance Properties and Age of the Baptistina Family

The Baptistina asteroid family resides in the same portion of orbital element space as the larger Flora family, and complete membership lists for both families cannot be obtained via common clustering methods due to cross-contamination and nonuniform phase space density. Here we use restrictive cuts in orbital element space to select out enhanced samples from both families to determine their color and albedo characteristics. We find the Baptistina family to have an average SDSS (a*, i-z) color of (-0.028 ± 0.006, -0.005 ± 0.015) and an average WISE visual albedo of 0.171 ± 0.006, distinguishing it as the only inner main belt family occupying this region of color-albedo parameter space. Having established the distinct reflectance properties, we next use cuts on color and albedo to select out a Baptistina-enhanced sample for further dynamical study. We determine the age of the family via two standard independent methods: 1) observations of the size-dependent drift in semimajor axis due to the combined influences of the Yarkovsky and YORP effects, and 2) observations of the spread in proper eccentricity and inclination due to chaotic diffusion. For method 1, we calibrate the Yarkovsky drift by scaling from clusters with similar physical parameters for which we have obtained independent measurement of the Yarkovsky drift rates, as an alternative to estimation of all of the physical parameters that affect the drift rates. We further estimate the magnitude of the influence on the drift rates due to obliquity changes caused by both “variable YORP” (Bottke et al., this meeting) and spin-orbit resonances in the Flora and Baptistina region (Rubincam et al. 2002, JGR 107; Vokrouhlicky et al. 2006, Icarus 184), which can affect estimates of the family’s age by up to a factor of two. For the Baptistina family, this work extracts reflectance properties, orbital distribution and age from the complex mix of families in this region of the main belt. This work was supported by an NSF GRF (MJD) and a Michigan Space Grant Consortium undergraduate fellowship (SJV).