tary bodies may differ because of conditions and processes that existed at the 

 time and location of their origin, or they may differ because of endogenic alter- 

 ation processes such as might occur from heating caused by 26 AI decay. The 

 capability of evaluating diversity among comets is a unique attribute of the 

 dust-collection approach. 



A major goal of solar system research is the direct return of a pristine come- 

 tary sample collected from a dedicated mission to a comet nucleus. However, 

 even when such advanced missions occur, they will be limited by cost to a small 

 number of bodies and will not adequately study the diversity question which can 

 be addressed by cosmic dust collection. The dust collection may also provide 

 new insights into existing meteorites by providing criteria for identifying pos- 

 sible cometary or presolar materials in existing collections of meteorites and 

 interplanetary dust. For example, the recent identification of meteorites from 

 the Moon was possible only because analyses of lunar samples had defined sev- 

 eral characteristic properties of lunar material. It is assumed that appropriate 

 analysis of meteorites and interplanetary dust particles collected via U2 aircraft 

 will continue and that collections can be made in low Earth orbit, but in addi- 

 tion it would be highly desirable to sample directly the source regions of the 

 interplanetary dust population. Those sources are comets and asteroids, with the 

 former believed to be by far the dominant source. Sample-return missions to 

 comets are currently under consideration and, although that topic is strictly 

 outside the scope of this report, its relevance and potential value to the Earth 

 orbital investigations justify reiteration of the importance of such a mission. 



Finally, a conceivable but remote possibility concerns the issue of pan- 

 spermia. If extraterrestrial microbes have been dispersed in space and make a real 

 contribution to the cosmic-dust population, they may be included in any col- 

 lected samples. Routine microscopic surveys of the collected particles could be 

 followed up by detailed nondestructive chemical analyses. In the event that a 

 number of putative microbes were detected, attempts at culturing them for 

 viability and reproduction could be considered. Because of contamination and 

 collection problems in space, it is probably best to conduct panspermia experi- 

 ments in the stratosphere where large numbers of particles can be obtained with 

 minimal contamination. Samples could be cultured directly on the collection 

 substrate and correlation of growth with an actual extraterrestrial particle would 

 be evidence for capture of an organism. 



4.3 Technical Approach 



The proposed new dust-collection experiments will require both particle 

 collection and measurement of orbital parameters. The trajectory and speed of 

 an incoming particle must be measured with sufficient precision so that a good 

 match can be made between the collected particle and the source body. The 

 orbits of dust particles evolve because of Poynting-Robertson drag, which 

 decreases the eccentricity and semimajor axis with time, but does not alter the 



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