TY - JOUR
T1 - High-albedo c-complex asteroids in the outer main belt
T2 - The near-infrared spectra
AU - Kasuga, Toshihiro
AU - Usui, Fumihiko
AU - Ootsubo, Takafumi
AU - Hasegawa, Sunao
AU - Kuroda, Daisuke
PY - 2013/7/1
Y1 - 2013/7/1
N2 - Primitive, outer-belt asteroids are generally of low albedo, reflecting carbonaceous compositions like those of CI and CM meteorites. However, a few outer-belt asteroids having high albedos are known, suggesting the presence of unusually reflective surface minerals or, conceivably, even exposed water ice. Here, we present near-infrared (1.1-2.5 μm) spectra of four outer-belt C-complex asteroids with albedos ≥0.1. We find no absorption features characteristic of water ice (near 1.5 and 2.0 μm) in the objects. Intimate mixture models set limits to the water ice by weight ≤2%. Asteroids (723) Hammonia and (936) Kunigunde are featureless and have (60%-95%) amorphous Mg pyroxenes that might explain the high albedos. Asteroid (1276) Ucclia also shows a featureless reflection spectrum with (50%-60%) amorphous Mg pyroxenes. Asteroid (1576) Fabiola shows a possible weak, broad absorption band (1.5-2.1 μm). The feature can be reproduced by (80%) amorphous Mg pyroxenes or orthopyroxene (crystalline silicate), either of which is likely to cause its high albedo. We discuss the origin of high-albedo components in primitive asteroids.
AB - Primitive, outer-belt asteroids are generally of low albedo, reflecting carbonaceous compositions like those of CI and CM meteorites. However, a few outer-belt asteroids having high albedos are known, suggesting the presence of unusually reflective surface minerals or, conceivably, even exposed water ice. Here, we present near-infrared (1.1-2.5 μm) spectra of four outer-belt C-complex asteroids with albedos ≥0.1. We find no absorption features characteristic of water ice (near 1.5 and 2.0 μm) in the objects. Intimate mixture models set limits to the water ice by weight ≤2%. Asteroids (723) Hammonia and (936) Kunigunde are featureless and have (60%-95%) amorphous Mg pyroxenes that might explain the high albedos. Asteroid (1276) Ucclia also shows a featureless reflection spectrum with (50%-60%) amorphous Mg pyroxenes. Asteroid (1576) Fabiola shows a possible weak, broad absorption band (1.5-2.1 μm). The feature can be reproduced by (80%) amorphous Mg pyroxenes or orthopyroxene (crystalline silicate), either of which is likely to cause its high albedo. We discuss the origin of high-albedo components in primitive asteroids.
KW - infrared: planetary systems
KW - minor planets, asteroids: general
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U2 - 10.1088/0004-6256/146/1/1
DO - 10.1088/0004-6256/146/1/1
M3 - Article
AN - SCOPUS:84879099109
VL - 146
JO - Astronomical Journal
JF - Astronomical Journal
SN - 0004-6256
IS - 1
M1 - 1
ER -