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Published Online March 20, 2008
Science DOI: 10.1126/science.1154340

Reports

Submitted on December 18, 2007
Accepted on March 6, 2008

Ancient Asteroids Enriched in Refractory Inclusions

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

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.; Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ 85721, USA.; Department of Earth and Planetary Sciences, American Museum of Natural History, New York, New York 11024, USA.
3 Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560, USA.
4 Institute for Astronomy, University of Hawaii, Hilo, HI, 96720, USA.
5 Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20560, USA. ; Department of Geological Sciences and Engineering, University of Nevada, Reno NV 89557, USA.

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

Calcium-, 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 µm absorptions, attributed to FeO-bearing aluminous spinel. Similar absorptions are present in telescopic spectra of several asteroids; modeling indicates these contain ~30±10% CAIs, 2-3 times that of any meteorite. Survival of these undifferentiated, large (50-100 km diameter) CAI-rich bodies argues 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, are likely less altered, and are more ancient than any known sample in our meteorite collection, making them prime candidates for sample return.




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