Refractory-Rich Asteroids: Concentrations of the Most Ancient Materials in the Solar System

Details Refractory-Rich Asteroids: Concentrations of the Most Ancient Materials in the Solar System Refractory-Rich Asteroids: Concentrations of the Most Ancient Materials in the Solar System

Oct 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.3301s&link_type=abstract

American Astronomical Society, DPS meeting #39, #33.01; Bulletin of the American Astronomical Society, Vol. 39, p.476

Astronomy and Astrophysics

Astronomy

Scientific paper

Refractory inclusions found within chondritic meteorites are the oldest rocks in our collections and include the first phases predicted to condense from nebular gases. They consist of a variety of components including Calcium-Aluminum-Rich Inclusions (CAI's). Among the minerals in CAI's only spinel (MgAl2O4) has significant absorptions features in near-infrared spectra. If even minor amounts of FeO are present spinel has a strong 2 µm absorption. In our on-going SpeX survey, we have identified several asteroid surfaces with spectra that are dominated by absorptions at 2 µm region, yet lack 1 µm features. These spectra are similar to two anomalous, dynamically related asteroids previously identified by Burbine et al. (1992), which were interpreted as spinel-rich and thereby linked to CAI's. Our data confirm these initial finding and extend them to three separate spinel-rich parent bodies, including several members from two distinct families. Therefore, spinel-rich asteroids can no longer be considered rare. The quality of the SpeX data also preclude spinel group minerals of igneous origins (i.e., chromite), strengthening the link to CAI's. In parallel, we have also initiated a program to collect spectra and fully petrographically characterize CAI's within the Allende meteorite. Spectral comparisons with CAI's reveal that these asteroids contain higher concentrations of refractory-rich materials than any known meteorite. The asteroids likely accreted at an earlier time or in regions of the nebula where refractory-rich material was more common. Their preservation may define the limiting concentration of refractory-rich materials above which melting occurred. These refractory-rich asteroids have the highest concentrations of the oldest materials known, making them important constraints on early Solar System processes and excellent candidates for future space exploration.
This research funded in part by NASA (NNX06AH69G/ JMS; NNG05GF39G/ HCC) and NSF (AST-0307688/ SJB). Thanks to T. Hiroi (Brown/RELAB) for carefully collecting our spectra of CAI's.

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