NEAR INFRARED SPECTROSCOPY

Figure 7. Graph of very near infrared (VNIR) spectroscopy of Granada material.

Figure 8. Graph of VNIR of Pallas and Ceres Reproduced from Gaffey et al. (1993).

Spectral reflectance of the Granada material was obtained at wavelengths from 0.35-2.5 mm. A significant amount of noise exists at the end of the spectral curve, due to detector interference (fig. 7). Also, a slight step exists at 0.37 nm, being due to detector variations at short wavelengths. The reflectance curve is somewhat flat, being consistent with the presence of oxides such as magnetite, ilmenite, and spinel (fig. 7). Moreover, a slight variation exists at higher wavelengths, probably reflecting the occurrence of calcium silicate. The Granada material has a spectral signature similar to a class B, G, or K asteroid. These asteroid bodies are presumably composed of clays and opaque mineral assemblages; characteristic of metamorphic altered carbonaceous chondrite meteorite analogs (Gaffey et al., 1993). Type B and G represent iron-poor hydrated silicates, suggesting a partially to highly leached CII-meteorite analog. (Gaffey et al, 1993). Type K is composed of olivine and opaque assemblages, representing a possible type CV3 and CO3 chondrites. (Gaffey et al, 1993). These analogs are hypothetical and only suggest relative interpretations, for there may not be representatives in the present meteorite collections (Gaffey et al, 1993). It is difficult to ascertain the possibility that the Granada material corresponds to such a parent body, for there is no data acquired in the ultraviolet spectrum or water absorption features at 3.0 mm (Larson and Veeder, 1979). Moreover, a large degree of uncertainty exists between laboratory-derived measurements of the Granada material and ground based observations of asteroids. Uncertainties in ground-based observations are a result of atmospheric disturbance and loss of data backscattered data. Asteroid spectroscopy results are often corrected to accommodate this variation in error, by normalizing the spectral reflectance to albedo patters and solar zenith angles (Nelson et al., 1993). The spectral reflectance matches that of a B, G, or K asteroid (fig. 8).The curves are all flat having low reflectance values, resembling that of oxide phases. Moreover, two small peak wavelengths occur at 0.71 mm and 2.15 mm, which is particularly characteristic of a type G asteroid. (fig. 8) Type G asteroids are characterized by several members within the asteroid belt, with Ceres being the largest and most well-known member. Type B asteroids also represent several members, including Pallas. Thus, it can be proposed that the Granada material represents a pristine type G asteroid parent body that has not undergone significant aqueous alteration. Larnite (Ca2SiO4) is chemically and structurally similar to monticellite (Ca2MgSiO4); where monticellite could be formed by aqueous alteration of larnite.