Chapter V 

 In Situ Investigations 



L. Allamandola, A. Bar-Nun, T. Brock, S. Chang, 



R. E. Davies, j. M. Greenberg, L. Hochstein, 

 G. Horneck, W. Huntress, S. Miller, K. Nealson, 



and D. Usher 



A spacecraft in Earth orbit provides a uniquely useful environment for studies 

 that are of central importance to modern exobiology. Such a space platform 

 makes available special conditions including microgravity, a reasonably good 

 vacuum with a very high pumping speed, a continuous source of high-energy 

 neutral atomic oxygen, and a solar flux that is less attenuated than that at the 

 Earth's surface. 



In this Chapter we discuss four different types of experiments that can be 

 performed on a space platform. These are the study of suspended grains, reac- 

 tions of neutral atomic oxygen, studies of an artificial comet, and possible 

 experimental tests of the viability of microorganisms in space. 



5.1 Models of Interstellar Grains 



Interactions between a gas phase and a solid phase are well known and 

 include sorption phenomena, heterogeneous catalysis, and many other familiar 

 terrestrial physical-chemical processes. Such interactions are also important in 

 the space environment, particularly for the roles they play in the cosmic history 

 of the biogenic elements and compounds. Elucidation of this history involves 

 tracing the physical and chemical pathways taken by the biogenic elements 

 and compounds from their origin in stars to their incorporation into preplane- 

 tary bodies, measuring the biogenic elements and compounds in the galaxy 

 and solar system to develop theories about the formation of the solar system, 

 and determining how the physical and chemical properties of the biogenic 

 elements and compounds influenced the formation of the solar system and the 

 bodies within it. In this context, interactions among gases and grains in space are 



Artist's concept of a laboratory module for the Space Station. 



89 



