Spectral properties and rotational spectral heterogeneity of 433 Eros

Composite spectra of different rotational aspects of the S asteroid 433 Eros were assembled from previous studies, covering the wavelength range 0.33-2.5 mu m. These data allow us to measure significant attributes of Eros's spectrum, its mafic mineral absorptions, and the degree and nature of compositional heterogeneity of its surface. We also evaluated previous S-asteroid taxonomies using independent methods, and from this test determined that the taxonomy of Gaffey et al. [1993] provides a sound basis for relating Eros to other S asteroids. On average, Eros resembles the S(IV) asteroids, which bear the closest resemblance to ordinary chondrites in mafic mineralogy. However, Eros also exhibits distinct rotational spectral variations comparable to the greatest yet recognized on an S asteroid. One side of the asteroid has a shorter-wavelength 1-mu m absorption and a stronger 2-mu m absorption than the global average, and is interpreted to be richer in pyroxene; the opposite face has a longer-wavelength 1-mu m absorption and a weaker 2-mu m absorption, and is interpreted to be richer in olivine. The pyroxene-rich side coincides with a facet-like face identified in radar studies, and the olivine-rich side coincides with a convex-shaped face. Each side of the asteroid exhibits spectral affinities with a different spectral class of S asteroids, demonstrating that such subdivisions of S asteroids represent different parts of a compositional continuum. High spatial resolution measurement of the mineralogic and elemental compositions and especially the geologic settings of these different materials by the Near-Earth Asteroid Rendezvous mission will provide a great advance in the understanding of the origin and evolution of a candidate ordinary chondrite parent body.