1. 1 Spectral and mineralogical diversity among the M-asteroids P.S. Hardersen 1, M.J. Gaffey 1, P.A. Abell 2, E.A. Cloutis 3, V. Reddy 1, S.K. Fieber-Beyer 1 1 University of North Dakota 2 NASA Johnson Space Center 3 University of Winnipeg

2. 2 M-type Asteroids Asteroids belonging to the taxonomic M-class have historically been identified based on relatively featureless spectra over visible wavelengths, and moderate albedos of ~20%. Based on these spectral properties, M-type asteroids have been interpreted as having a metallic (Fe-Ni) or enstatite chondritic surface composition. These asteroids have often been thought to be core fragments of once-larger differentiated parent bodies, exposed over time through collisional processes. Extending the study of M-type asteroids into the near-IR will improve our understanding of the compositions of these objects.

3. 3 IRTF: M-asteroid research Low-Fe pyroxene feature. Olivine feature. CV/CO- chondrite analogue?

4. 4 IRTF: M-asteroid research April 2005: Hardersen et al. (2005) show that six of eight M- asteroids have weak ~0.9-micron absorption features. Primary interpretation: Features caused by surface low-Fe pyroxenes. March 2006 (LPSC): Additional M-asteroids show spectral evidence of: 1.low-Fe pyroxene on additional asteroids. 2.weak olivine spectral features. 3.spectra similar to CO/CV-chondrites. 4.weak spinel-like features.

5. 5 IRTF: M-asteroid research Implications: The surface mineralogies of the Tholen M-asteroid group are spectrally and mineralogically diverse. Thus M- asteroids include objects with varying geological and thermal histories. January 2007: Data have been obtained on 39 of the 47 Tholen M-asteroids with the IRTF/SpeX. Should obtain ~100% M- asteroid spectra by the conclusion of this program. Application: M-asteroid spectra and interpretations are useful for understanding the thermal history of the main asteroid belt.