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Originally published in Science Express on 20 March 2008
Science 25 April 2008:
Vol. 320. no. 5875, pp. 514 - 517
DOI: 10.1126/science.1154340
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Reports

Ancient Asteroids Enriched in Refractory Inclusions

J. M. Sunshine,1* H. C. Connolly, Jr.,2,3,4 T. J. McCoy,5 S. J. Bus,6 L. M. La Croix5,7

Calcium- and aluminum-rich inclusions (CAIs) occur in all classes of chondritic meteorites and contain refractory minerals predicted to be the first condensates from the solar nebula. Near-infrared spectra of CAIs have strong 2-micrometer absorptions, attributed to iron oxide–bearing aluminous spinel. Similar absorptions are present in the telescopic spectra of several asteroids; modeling indicates that these contain ~30 ± 10% CAIs (two to three times that of any meteorite). Survival of these undifferentiated, large (50- to 100-kilometer diameter) CAI-rich bodies suggests that they may have formed before the injection of radiogenic 26Al into the solar system. They have also experienced only modest post-accretionary alteration. Thus, these asteroids have higher concentrations of CAI material, appear less altered, and are more ancient than any known sample in our meteorite collection, making them prime candidates for sample return.

1 Department of Astronomy, University of Maryland, College Park, MD 20742, USA.
2 Department of Physical Sciences, Kingsborough Community College of the City University of New York, Brooklyn, NY 11235, USA.
3 Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.
4 Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY 11024, USA.
5 Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC 20560, USA.
6 Institute for Astronomy, University of Hawaii, Hilo, HI 96720, USA.
7 Department of Geological Sciences and Engineering, University of Nevada, Reno, NV 89557, USA.

* To whom correspondence should be addressed. E-mail: jess{at}astro.umd.edu

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