2008 Annual Science Report
University of Hawaii, Manoa Reporting | JUL 2007 – JUN 2008
The Main Belt Distribution of Basaltic Asteroids
We have provided constraints on the distribution of basaltic asteroids in the main asteroid belt. Basaltic asteroids are fragments of larger bodies that reached high enough temperatures at the time of their formation that they melted and differentiated into a metallic core and a basaltic/silicate mantle and crust. This these asteroids trace the thermal processes that affected protoplanetary material during the epoch of planet formation in the Solar System.
We present the observational results of a survey designed to target and detect asteroids whose colors are similar to those of Vesta family members and thus may be considered as candidates for having a basaltic composition. Fifty basaltic candidates were selected with orbital elements that lie outside of the Vesta dynamical family. Optical and near-infrared spectra were used to assign a taxonomic type to 11 of the 50 candidates. Ten of these were spectroscopically confirmed as V-type asteroids, suggesting that most of the candidates are basaltic and can be used to constrain the distribution of basaltic material in the Main Belt.
Using our catalog of V-type candidates and the success rate of the survey, we calculate unbiased size-frequency and semi-ma jor axis distributions of V-type asteroids. These distributions, in addition to an estimate for the total mass of basaltic material, suggest that Vesta was the predominant contributor to the basaltic asteroid inventory of the Main Belt, however scattered planetesimals from the inner Solar System (a < 2.0 AU) and other partially/fully differentiated bodies likely contributed to this inventory. In particular, we infer the presence of basaltic fragments in the vicinity of asteroid 15 Eunomia, which may be derived from a differentiated parent body in the middle Main Belt (2.5 < a < 2.8). We find no asteroidal evidence for a large number of previously undiscovered basaltic asteroids, which agrees with previous theories suggesting that basaltic fragments from the ~ 100 differentiated parent bodies represented in meteorite collections have been “battered to bits” [Burbine, T.H., Meibom, A., Binzel, R.P., 1996. Mantle material in the Main Belt: Battered to bits? Met. & Planet. Sci. 31, 607].