Extracting Spectral Information about 253 Mathilde Using the NEAR Photometry

Abstract

The Near Earth Asteroid Rendezvous (NEAR) spacecraft will conduct the first photometric imagery of a C-class asteroid when it flies by 253 Mathilde. An absorption feature seen in ground-based disk-integrated spectra of many C-class asteroids has been attributed to oxidized iron in phyllosilicate minerals of the serpento-chlorite groups. We have designed a method of identifying this absorption feature in the NEAR photometry of Mathilde. A linear mixing model was used to combine two sets of synthetic NEAR photometry created from a spectrum of Mathilde that does not show this feature and the average of nine spectra of other C-class asteroids each having the 0.7-μm absorption feature. We find that a spatial unit must contain a minimum of 55% material that has a spectrum showing the 0.7-μm absorption feature for the presence of this material to be spectrally detectable in the NEAR photometric imaging data.