Compositional properties of Near-Earth Asteroids: spectroscopic comparison with Ordinary Chondrite Meteorites.

Some years ago we started a spectroscopic survey, in the visible region, of Earth-approaching asteroids to investigate their compositional nature in order to improve the comprehension of their origin. To date we have obtained low-resolution spectra, in the range 0.5-1.0μm, of 1 Aten (3753 1986 TO), 4 Apollo (1864 Daedalus, 5786 Talos, 1989 JA, 2063 Bacchus), and 3 Amor (3352 McAuliffe, 4954 Eric, 5836 1993 MF). Most of them show spectra similar to those of the S taxonomic class; Bacchus only has a spectrum which resembles those of more primitive objects (C-type). It has not been possible to definitively distinguish to which S-subclass the observed objects belong because the spectra we obtained do not cover the necessary spectral range to make this investigation as described by Gaffey et al. (1993Icar..106..573G). Nevertheless four of the observed objects have visible spectra similar to those of ordinary chondrites meteorites suggesting a strong relation between the two classes of objects. Moreover 5836 1993 MF shows an absorption feature near 6000Å probably due to the presence of aqueous altered materials.