main belt and at the orbit of Jupiter. Evidence has been presented that the car- 

 bonaceous materials in comets might be similar to this D-material. The spectral 

 characteristics of the D-material have been defined poorly, and high-resolution 

 spectrometry in the infrared would help constrain its composition and test avail- 

 able speculations concerning its nature. There is a tendency to regard D-material 

 as a less "processed" version of what becomes C-material, but such vague sugges- 

 tions need to be tested. 



A fundamental question in dealing with carbonaceous material in the solar 

 system concerns the possible interrelationship of comets and some types of 

 asteroids. It has long been suspected that some comets must evolve into objects 

 resembling Earth-crossing asteroids. Two recent observations have added circum- 

 stantial support to this general view. The first was the discovery by IRAS of a 

 small, asteroid-like body (1983 TB) whose orbit is closely similar to the Geminid 

 meteor stream. The second was the discovery of disturbances in the solar wind 

 that might be attributed to the release of volatile material from the Apollo 

 asteroid 2201-Oljato. Several Earth-crossers have been identified as likely dead 

 comets on the basis of their orbital characteristics. Thus, an important problem 

 is how to identify the dead comets among the population of Earth-crossers 

 (from orbital or remote-sensing observations) and then to obtain high-resolution 

 spectra of their surfaces for comparison with meteorite samples and other solar 

 system small bodies. Another opportunity for understanding the interrelation- 

 ships may arise from a study of meteor showers. 



Current measurements of the properties of comets constrain the abundances 

 of volatile materials; the refractory component abundances must be inferred by 

 other means. This may be possible from measurements of the ultraviolet spectra 

 of meteor showers associated with active and extinct comets. Because many 

 meteors are too fragile to survive passage through the Earth's atmosphere, such 

 spectroscopic measurements are the only method by which elemental abundance 

 ratios for a large number of known cometary samples can be determined. 

 Ground-based optical efforts have not been sufficiently quantitative because of 

 the large number of iron lines that mask other interesting features. There are 

 several "iron-free" windows in the ultraviolet (1150-1250 A, 1300-1350 A, 

 1370-1550 A, 1800-1900 A, 1970-2080 A) through which lines of H, C, SiO, 

 P, S, N, O, Al, Mg, Mn, Ca, Na, and Zn may be strong enough to be visible from 

 low-Earth-orbit observations of meteor streams. If practical, such observations 

 might be conducted from a dedicated instrument launched from the Shuttle or 

 an ELV, or from one of the polar-orbiting platforms associated with the Space 

 Station composed primarily of Earth-observing instruments. This may provide 

 additional data to combine with inventories of meteoritic abundances and help 

 identify the dead cometary component among the Earth-crossing asteroids. 



A summary of important measurements to be taken and questions to be 

 answered follows: 



1. High-spectral-resolution infrared (1 to 5 jum) spectra of C-asteroids and 



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