Chapter IV 

 Cosmic Dust Collection 



D. Brownlee, T. Bunch, S. Chang, J. Kerridge, 



and J. Wolfe 



Primitive solar system objects such as asteroids and comets occupy an impor- 

 tant place in exobiology because their contents include water, organic matter, 

 and minerals that, together, are considered prerequisites for the prebiotic evolu- 

 tion of biological materials from chemical systems. In addition, these materials 

 are samples of planetesimals that contributed some fraction of the volatile con- 

 tents of the terrestrial planets. They also contain abiotic organic compounds and 

 carbonaceous materials that may be attributed to origins in the parent bodies, 

 the solar nebula, and galactic environments that preceded the nebula. Therefore, 

 their origins and the origins of their components have a bearing on understand- 

 ing the cosmic evolution of biogenic compounds and the development of models 

 for prebiotic evolution on planets. To asteroids and comets, however, should be 

 added a third category of materials of exobiological interest, "cosmic dust," 

 the information about the content of which shows promise of supplementing 

 and complementing that of the first two types of material. 



The designation cosmic dust is applied to extraterrestrial particles less than 

 1 millimeter in diameter. Some of these particles that have entered Earth's 

 atmosphere have been collected by high-flying aircraft. It is believed that most 

 are debris from comets and asteroids that predate our planetary system and may 

 have thus originated outside the solar system. Isotopic anomalies in primitive 

 carbonaceous meteorites suggest that dust originating from their cometary or 

 asteroidal parent bodies contains components formed in the presolar epoch. In 

 any case, cosmic dust should be viewed as possible samples of primordial 

 material that have been preserved since the early history of the solar system. 

 In the exobiological context, laboratory studies of the biogenic elements and 

 compounds in these minute objects will open windows through which physical 

 and chemical processes operating in the galaxy or early solar system may be 



Scanning Electron Micrograph of a porous chondritic micrometeorite collected in 

 the stratosphere by a NASA Ames U-2 aircraft. 



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