THE FIRST CONFIRMATION OF A COMMON ORIGIN FOR A SMALL V-CLASS ASTEROID WITH 4 VESTA AND THE HED METEORITES

Analysis of a new, near-infrared spectrum for 1929 Kollaa allows us to determine not only that this mainbelt asteroid is a daughter of 4 Vesta, but also to constrain the location of its formation within Vesta and its connection to a group of meteorites. The depth, width, and spectral placement of the 1- and 2-mm mafic silicate absorption features in the ground-based reflectance spectrum of 4 Vesta (the archetype V-class asteroid) indicate that orthopyroxene is a major phase in its surface mineralogy. In 1994 and 1996, Hubble Space Telescope observations confirmed albedo differences across Vesta's surface, and produced shape and topographic information about Vesta. Dynamical studies previously revealed that a family of mainbelt asteroids is associated with 4 Vesta. Taxonomic surveys have found numerous, smaller asteroids with Vesta-like 1-mm spectral absorption features. To date, work on the surface mineralogy of Vesta was the definitive analysis for one of these V-class asteroids since no complete near-infrared spectrum of another V-type has existed. The case for a Vesta-HED meteorite connection has a firm mineralogical foundation. Previous spectral data have suggested a link to additional V-class asteroids, but until now that supposed association has not been mineralogically tested. We present a near-infrared reflectance spectrum of asteroid 1929 Kollaa obtained at the NASA Infrared Telescope Facility covering the critical 1- and 2-mm absorption features. Parameters derived from these features yield values for the orthopyroxene composition and plagioclase-to-orthopyroxene abundance ratio that fall well within the range for basaltic achondrites and 4 Vesta. Additional spectral parameters allow us to further constrain the orthopyroxene composition of 1929 Kollaa, which is consistent with that of cumulate eucrites. This demonstrates that 1929 Kollaa formed deep in the eucritic crust of Vesta near the diogenitic zone. Furthermore, it establishes the first mineralogical (genetic) connection between a Vesta-region asteroid with both 4 Vesta and a subset of the HED meteorites.