The distribution of basaltic asteroids in the Main Belt

Abstract

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-major 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.

An extension of the Bus asteroid taxonomy into the near-infrared

“…Most V-class asteroids that have been discovered are among the Vesta family and are known as Vestoids, although a few other objects have been identified throughout the main belt, such as 1459 Magnya (Lazzaro et al, 2000) and objects from the basaltic asteroid survey by Moskovitz et al (2008). The R-class, created for its sole member 349 Demboska by Tholen (1984), is similar to the V-class in that it displays deep 1-and 2-μm features, however the one- Similarly, many Bus S, Sq, and Sk objects become less clearly separated when their spectra extend to the near-infrared.…”

More chips off of Asteroid (4) Vesta: Characterization of eight Vestoids and their HED meteorite analogs

“…The consequence of this is that an asteroid's taxonomic classification only provides broad constraints for an asteroid's composition that requires additional diagnostic efforts (i.e., NIR spectra) to define surface mineralogy and potential meteorite analogs. The low 9% false positive rate suggests that the V-type taxonomy provides a relatively good method for identifying basaltic asteroids (Roig and Gil-Hutton, 2006;Moskovitz et al, 2008). However, this false positive rate is only valid for a small sample size of 21 asteroids (Roig and Gil-Hutton, 2006;Moskovitz et al, 2008).…”

“…Previous visible-and near-infrared (VNIR) spectral work on V-type asteroids has produced a false positive rate of ~9%, where a false positive represents a taxonomically classified V-type asteroid that does not exhibit basaltic surface mineralogic characteristics in its VNIR spectrum (Roig and Gil-Hutton, 2006;Moskovitz et al, 2008).…”

“…The low 9% false positive rate suggests that the V-type taxonomy provides a relatively good method for identifying basaltic asteroids (Roig and Gil-Hutton, 2006;Moskovitz et al, 2008). However, this false positive rate is only valid for a small sample size of 21 asteroids (Roig and Gil-Hutton, 2006;Moskovitz et al, 2008). Obtaining a more robust false positive rate for the V-type main-belt asteroid population will better determine the usefulness of the V-taxonomic class, while also identifying those basaltic asteroids that are directly (i.e., dynamically, spectrally, and mineralogically) associated with (4) Vesta and those V-type asteroids in the outer main belt that are basaltic.…”

“…The derivation of spectral band parameters, and the comparison of those band parameters with those from representative samples from the Howardite-Eucrite-Diogenite (HED) meteorite types, allows a direct comparison of their primary mineralogies. Establishing tighter constraints on the genetic Vestoid population will better inform mass estimates for the current population of probable Vestoids, will provide more accurate orbital information of Vestoid migration through time that will assist dynamical models, and will constrain the Icarus, accepted for publication, August 12, 2014 3 overall current abundance of basaltic material in the main asteroid belt (Moskovitz et al, 2008). …”