Olivine-dominated A-type asteroids in the Main Belt: Distribution, Abundance and Relation to Families

1Francesca E.De Meo,2David Polishook,3Benoît Carry, 4Brian J.Burt, 5,6Henry H.Hsieh,1Richard P.Binzel, 4A.Moskovitz, 7Thomas H.Burbine
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2018.12.016]
1Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 USA
2Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 0076100, Israel
3Observatoire de la Cte d’Azur, Boulevard de l’Observatoire, 06304 Nice Cedex 4, France
4Lowell Observatory, 1400 West Mars Hill Road, Flagstaff, AZ 86001, USA
5Planetary Science Institute, 1700 E. Ft. Lowell Road, Suite 106, Tucson, AZ 85719, USA
6Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 10617, Taiwan
7Department of Astronomy, Mount Holyoke College, South Hadley, MA 01075, USA
Copyright Elsevier

Differentiated asteroids are rare in the main asteroid belt despite evidence for  ∼ 100 distinct differentiated bodies in the meteorite record. We have sought to understand why so few main-belt asteroids differentiated and where those differentiated bodies or fragments reside. Using the Sloan Digital Sky Survey (SDSS) to search for a needle in a haystack we identify spectral A-type asteroid candidates, olivine-dominated asteroids that may represent mantle material of differentiated bodies. We have performed a near-infrared spectral survey with SpeX on the NASA IRTF and FIRE on the Magellan Telescope.
We report results from having doubled the number of known A-type asteroids. We deduce a new estimate for the overall abundance and distribution of this class of olivine-dominated asteroids. We find A-type asteroids account for less than 0.16% of all main-belt objects larger than 2 km and estimate there are a total of  ∼ 600 A-type asteroids above that size. They are found rather evenly distributed throughout the main belt, are even detected at the distance of the Cybele region, and have no statistically significant concentration in any asteroid family. We conclude the most likely implication is the few fragments of olivine-dominated material in the main belt did not form locally, but instead were implanted as collisional fragments of bodies that formed elsewhere.

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