Spectral and mineralogical diversity among the M-asteroids

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Spectral and mineralogical diversity among the
M-asteroids

• P.S. Hardersen1, M.J. Gaffey1, P.A. Abell2, E.A.
  Cloutis3, V. Reddy1, S.K. Fieber-Beyer1
• 1 University of North Dakota
• 2 NASA Johnson Space Center
• 3 University of Winnipeg

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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.

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IRTF M-asteroid research
Olivine feature.
Low-Fe pyroxene feature.
CV/CO-chondrite analogue?
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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
• low-Fe pyroxene on additional asteroids.
• weak olivine spectral features.
• spectra similar to CO/CV-chondrites.
• weak spinel-like features.

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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.