One known difficulty with spectral-reflectance measurements is that it can 

 be difficult to derive uniquely and accurately the relative abundances of key 

 constituents if one does not know a priori the whole suite of materials present 

 and the texture of the regolith. This problem is especially acute when dealing 

 with the abundances of optically opaque materials (metallic nickel/iron, magne- 

 tite, carbonaceous material). This is a major contributing factor to disagreements 

 in the literature over the metallic content of S-asteroid surfaces and the rela- 

 tionship of dark asteroids such as Pallas to carbonaceous chondrites. 



One major question concerns the types and distributions of organic-rich and 

 volatile-rich materials that formed in the solar system as a result of direct con- 

 densation from the solar nebula or aggregation from primitive presolar dust, or 

 subsequent processing on or within parent bodies. Several types of parent bodies 

 are involved-main-belt asteroids, Trojan asteroids, small satellites of the outer 

 planets, and comets. Each population of parent body has experienced its own 

 long history of evolution and it is difficult to infer the original characteristics 

 from what we observe today. Is any interrelationship that we observe representa- 

 tive of that which obtained in the early stages of the solar system? A particular 

 difficulty is that our only compositional information on distant objects comes 

 from remote-sensing data that refer only to the surfaces of these bodies. How do 

 we relate the surface composition to internal bulk characteristics or to the 

 detailed properties of meteorite samples measured in the laboratory? 



One important investigation would involve a concerted effort to define the 

 inventory of carbonaceous materials in the solar system, as a prelude to deter- 

 mining its precise composition and ultimately its provenance and history. From 

 the study of meteorites it is clear that several types of carbonaceous materials 

 are present. Some of this material has undergone evident processing on parent 

 bodies and it is suspected that most of these parent bodies were asteroidal rather 

 than cometary in origin. Whether or not any carbonaceous meteorites could be 

 derived from comets remains an issue of current debate. 



Spectral-reflectance measurements in the near infrared have made it possible 

 to identify certain asteroid surface materials with carbonaceous meteorite 

 analogs: for example, 1 -Ceres has been associated with a CI or CM carbonaceous 

 chondrite. It is evident from such observations that the surfaces of C-asteroids in 

 the main belt vary in the strength of the 3-/um absorption feature attributed to 

 water-of-hydration in the clay minerals that make up these materials. In general, 

 such measurements are difficult to make and require high sensitivity and high 

 resolution. Since it appears possible to relate the strength of the 3-jum feature to 

 carbonaceous meteorite mineralogy, an important goal of asteroid research 

 should be to establish how widespread such material is and to determine the 

 strength of this feature for as many C-asteroids as possible. 



The carbonaceous material associated with asteroids in the outer solar system 

 is different spectrally from that in many of the bodies in the asteroid belt. A 

 distinction has been made between the C-material in the main belt and the 

 D-material (very dark, but redder) that is found in the outer fringes of the 



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