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Unformatted text preview: Asteroids Detected as streaks in photographs with long exposure times. Over 150,000 have been catalogued Orbits are more elliptical and inclined than those of most planets Strong gaps and peaks in the periods (and therefore radii) of the orbits, due to resonances with other planets (primarily Jupiter). Largest asteroid is Ceres First asteroid detected (1801) Large enough that self-gravity creates a spherical shape Other asteroids range in size probably down to microscopic scales But total mass only corresponds to about the mass of Pluto Sizes and Shapes The optical brightness of an asteroid is due to reflected sunlight. Brightness is related to asteroid size, but also to distance and albedo: 2 2 2 ) ( d R r f A f Sun V ref Need to know how much sunlight is absorbed Absorbed sunlight is reradiated in the infrared (asteroids are cold) 2 2 4 ) ( ) 1 ( d R r f A f Sun V th Thus comparing infrared and optical luminosity tells us the albedo V V th ref A A f f 1 2...
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- Winter '09