In the subsequent sections of this chapter, specific examples are presented 

 of the kinds of data that would be most useful for exobiology. From a study of 

 the type of instrumentation that will probably be available in orbit (described in 

 Appendix B), the members of the Workshop have concluded that many of these 

 data should be obtainable in the near future. Attempts have been made to 

 identify those areas in which modification of planned instrumentation would be 

 desirable. The individual subsections are organized so that each one discusses 

 problems relating to a particular astrophysical environment. They are ordered 

 with respect to distance, starting with those closest in our own solar system and 

 progressing outward to studies of external galaxies. Chapter 6 provides a priori- 

 tized summary of the various observational projects discussed in all of these 

 subsections. 



Suggestions for Further Reading 



Harwit, M.; and Neal, V.: The Great Observatories for Space Astrophysics. 

 NASA Astrophysics Division, Washington, 1985. 



European Space Science Horizon 2000. ESA SP-1070, 1984. 



3.3 Planetary Atmospheres 



What useful exobiological information can be obtained from the study of 

 planetary atmospheres? Although little can be learned about actual local biology 

 (should it exist) through comparative studies of the planets and their atmo- 

 spheres, much can be learned about the formation and properties of environ- 

 ments that may be necessary for life and, by extension, about the development 

 of our own environment. Information about environments in which life arose in 

 the solar system and those in which it apparently did not will provide con- 

 straints on the conditions favorable for the origin of life and, by implication, the 

 likelihood of the existence of such environments and life elsewhere. At the most 

 general level, we want to understand the chemistry of the biogenic elements and 

 compounds in the solar system at the present time as well as in the past. Some 

 basic problems are summarized by the following questions: 



1. From what did the planets form; what can the planets and their atmo- 

 spheres tell us about the primordial, pre-solar nebula? 



2. How did the planets form? Did they form by simple gravitational collapse 

 of parts of the nebula or by accretion of grains? What does this say about the 

 possible existence of planets suitable for life in other stellar systems? 



3. What are the conditions necessary for the stable existence of the different 

 atmospheres found in the solar system, and how did they form? 



4. How have these atmospheres evolved since their initial formation? This 



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