Mineralogical Variations on the Surfaces of Low-Albedo Asteroids
Catherine A. Thibault, Denison University; Faith Vilas, NASA JSC; Scott A. Sawyer, University of Texas; Alan Fitzsimmons, Queen's University of Belfast
Narrowband reflectance spectra (approx. 0.5-0.9mm) of 24 low-albedo asteroids with known rotational periods were examined for variations in surface mineralogical composition with location across the asteroid's surface. For each object, spectral observations were obtained on more than one night. With the pole orientations largely unknown, we assumed that each asteroid was oriented with its rotational axis perpendicular to the line of sight of the telescope. We determined that surface observation positions ranged by object form observations of the same location to observations of the same sides of an asteroid. Most asteroids showed no significant variation among spectra of different locations across the asteroid's surface. Spectra of 5 asteroids showed variations that we considered significant. Asteroid 444 Gyptis (C) showed the 0.7-mm absorption feature attributed to iron-bearing phyllosilicates on one side, with no feature present on the other side. Spectra of 51 Nemausa (CU) showed variation in the depth of the 0.7-mm absorption feature. Spectra of 375 (Ursula (C) and 914 Palisana (CU) showed evidence for the 0.7-mm feature in one or more locations and the 0.65-mm feature in another location. Asteroid 52 Europa (CF) showed the 0.65-mm feature varying with location.