'Wet' E and M class asteroids

Details 'Wet' E and M class asteroids 'Wet' E and M class asteroids

Jul 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994metic..29q.450b&link_type=abstract

Meteoritics (ISSN 0026-1114), vol. 29, no. 4, p. 450

Other

1

Abundance, Albedo, Asteroids, Chemical Composition, Meteorites, Silicates, Absorption Spectra, Hydroxyl Radicals, Infrared Spectra, Metallicity, Mineralogy, Spectral Reflectance, Water

Scientific paper

The E and M asteroid classes have very similar red-sloped featureless spectra in the visible and near-IR wavelengths. It is their differences in albedo that form the basis for distinguishing these classes. The M class displays a moderately high albedo and the surface material of these asteroids is interpreted to be composed of Fe-Ni metal. The E class has a high albedo and the mineralogy of these asteroids is interpreted to be dominated by enstatite. However, over the past decade observational evidence has been accumulating indicating that at least some of the M asteroids may not be metallic and some of the E asteroids may not be enstatite. Radar, polarimetry, thermal-infrared, and near-infrared studies have suggested that at least some members of the M class have silicate mineralogies rather than the Fe-Ni compositions that are usually associated with this class. The 3.0-micron absorption band in volatile-rich meteorites is typically caused by a combination of the very strong fundamental absorptions of the absorbed H2O and structural interlattice OH molecules. The depth of the H2O/OH feature depends on many parameters besides abundance of H2O/OH, including particle size, albedo, and temperature. However, a band as strong as the one seen in the 44 Nysa spectra would require at least 2-5 wt% H2O/OH if it were in volatile-rich meteorites. To produce this hydration feature, hydrated minerals must make up a substantial and perhaps dominant fraction of the surface material of Nysa. Hydrous E and M asteroids may represent new classes of asteroids that have surface mineralogies unlike anything so far seen in the meteorite collections. Observations imply that the hydrated E and M asteroids have very little in common with the other anhydrous members of their taxonomic classes that are probably igneous (E and M asteroids) and metal-rich (M asteroids).

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