LYCOS RETRIEVER 
Asteroids: Sun
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Asteroids are ... classified by composition and albedo, most being one of three types. The majority (C-type) are similar to carbon-chrondite meteorites with approximately the same composition as the sun (excluding hydrogen) and are relatively dark. Those with a composition of nickel iron mixed with silicates of iron and magnesium (S-type) are relatively bright. The M-type are composed of nickel iron and are bright. Some of the Trojan asteroids appear to be captured comets, composed of ice and dirt, rather than rocky asteroids.
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The fact that visually dark objects - such as asteroids - are better detected in the infrared might explain the discrepancy between visible and infrared results. For an optical telescope, the brightness of an asteroid depends on the visible light it reflects from the Sun.
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Going in the other direction, there are ... asteroids on the other side of the belt. Centaur asteroids are those that lie between 5.5 and 25 A.U. from the sun; there are approximately 85 Centaur asteroids known.
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The outer belt, which includes asteroids 250 million miles beyond the Sun, consists of rocky asteroids. These asteroids appear darker than the asteroids of the inner belt, and are rich in carbon.
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