106 



SOLAR SYSTEM 



The record of the early history of the solar system may be pre- 

 served in the organic and inorganic matter of the comets. Present 

 evidence is consistent with two possible scenarios for the origin of 

 the organic molecules sublimating from the cometary nucleus. Either 

 they represent the "frost" of interstellar molecules that condensed 

 onto those interstellar grains that have later accreted into comets, or 

 they represent the "snows" that condensed onto silicate grains dur- 

 ing the cooling phase of the presolar nebula. If they represent the 

 frost of interstellar molecules, we must obtain a more detailed under- 

 standing of what this frost is. To accomplish this we propose to 

 elucidate the major processes (stellar, circumstellar, interstellar, etc.) 

 involved in the formation of gaseous organic molecules detected in 

 interstellar space. For example, is the formation of much more 

 complex solid polymeric organic molecules possible in interstellar 

 dust-ice grain surfaces? How could they be detected? 



In addition, we need to acquire new and improved receivers at 

 millimeter and submillimeter wavelengths, and new, accurate, and 

 large telescopes to collect these wavelengths. Unavailable funds in 

 this area would likely set the United States back in its worldwide 

 lead in the study of the interstellar molecules during the 1980s. 

 Therefore, a greater effort should be exerted to convince the Govern- 

 ment of the significance of these research tools. 



However, if the comets represent the snows that condensed dur- 

 ing the primitive solar nebula, then the organic and inorganic con- 

 stituents would record for us the composition of the early solar 

 system. 



We can't go on much longer without knowing more about 

 comets. Even if these objects did not bring biomonomers to the sur- 

 face of the primitive Earth, they may have been a major source of 

 the volatile elements from which these compounds were later 

 formed. We need to study comet nuclei with a rendezvous mission 

 that brings a spacecraft close enough to permit detailed measure- 

 ments of the nucleus and inner coma. The program should build 

 toward a capability for sample return and interception of a large, 

 active comet that is approaching the inner solar system for the first 

 time. 



