Orbital and physical characteristics

Although here we are most interested in the chemical compositions of ice-bearing planetesimals, we will first briefly review their orbital and physical characteristics, so as to provide some context for the discussion of chemistry to follow. 

Several classes of asteroids are also thought to contain ices presently, or contained them at some earlier time. The D- and F-class asteroids occur in the outmost main belt, and the C-, G-, B-, and F-class asteroids are concentrated within the central part of the belt. These asteroids probably formed near their present locations, in which case they represent icebearing planetesimals that accreted inside the orbit of Jupiter. A few asteroids exhibiting cometary activity also occur within the asteroid belt. 

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