planets, exobiologists would no doubt wish to study them in detail. This will 

 require a whole new generation of telescopes or arrays of telescopes in high orbit 

 or on the lunar far side with capabilities in excess of the near-term orbiting 

 systems. There is much to be learned. 



6.2 Cosmic Dust Collection 



Collection of cosmic dust is important to exobiology because collectable dust 

 particles are samples of comets and asteroids, primitive bodies that are likely to 

 preserve compounds that formed during or before the origin of the solar system. 

 Cometary particles are of particular interest because comets probably formed in 

 the coldest, most-remote, regions of the solar nebula. Collection from Earth 

 orbit can provide an unbiased sample of nanogram to microgram particles 

 that complement meteorites and samples of extraterrestrial dust in the strato- 

 sphere. The most exciting aspect of meteoroid collection from orbital platforms 

 is the active measurement of impact velocity and directions to identify the 

 sources of individual collected particles. 



6.2.1 Capture Techniques 



The unintentionally captured meteoroids collected from returned Solar Max 

 surfaces have shown that analyzable material can be collected even with simple 

 materials such as aluminum sheet metal and multilayer plastic thermal blankets. 

 Capture experiments were recently flown on Salyut and currently are being 

 exposed on LDEF. They were specifically designed to collect meteoroids, and 

 their results will play a role in developing future experiments. The development 

 of special capture materials or cells for the collection of the biogenic material in 

 analyzable form is needed for exobiology. For example, special metal capture 

 cells where low-atomic-weight elements could be recondensed on cell walls fol- 

 lowing hypervelocity impact could be used— retention of some elements may 

 require a "getter." The development of clean cells made of appropriate materials 

 should lead at least to the capture of enough material to determine elemental 

 hydrogen, carbon, and nitrogen abundances and isotope ratios. The hydrogen 

 isotopic composition is of particular importance because large isotope effects 

 have been seen for this element in interplanetary dust samples. No previous 

 experiments exist for the capture of light elements, and the development of 

 capture cell techniques will involve laboratory simulation experiments (using 

 dust accelerators and lasers) and actual orbital collection experiments. 



The ultimate particle collection experiment is the so-called "intact capture" 

 in which the particle, or at least parts of the particle, are collected without heat- 

 ing or significant modification. One approach is to use "soft" collection sub- 

 strates where the particle is decelerated slowly. Soft materials include porous 

 targets and gas cells. Experiments under way are promising; porous targets can 



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