IMPROVING M-ASTEROID SPECTRAL INTERPRETATIONS VIA THE DETECTION OF WEAK ABSORPTION FEATURES
Although mineralogic diversity should be expected within an asteroid taxonomic group (Gaffey et al. 1993), recent interpretations have widely different implications for the histories of particular asteroids. For example, if an M-asteroid is interpreted as consisting of phyllosilicate minerals, this suggests a relatively low-temperature thermal history promoting aqueous alteration processes. If a NiFe metal and/or mafic silicate surface composition is suggested, then this often implies a higher-temperature environment and a more thermally-evolved asteroid.
Initial work by Hardersen (2003) and Hardersen et al. (2002) reveal the presence of weak, ~2-4% deep spectral absorption features in the ~0.9-micron region for asteroids 69 Hesperia, 110 Lydia, 201 Penelope and 216 Kleopatra. These authors interpret these asteroids as consisting of minor Fe- and Ca-poor orthopyroxenes surrounding the metallic cores of differentiated, disrupted parent bodies.
Full-rotational, near-infrared spectral observations of 16 Psyche, 125 Liberatrix and 136 Austria were obtained on March 22nd and 23rd, 2002, at the NASA Infrared Telescope Facility. Spectra for each asteroid will be examined for the presence or absence of any weak absorption features. Interpretations for each asteroid will be discussed and compared with the interpretations of previous workers.