Life Sciences in the Space Program 



scientifically rigorous, and well-coordinated program of research. Implementation 

 of such a program may be expected to yield major advances toward elucidating 

 the following: 1) the relationship between the organic matter of interstellar clouds 

 and primitive solar system bodies, such as comets and asteroids, and the 

 processes of prebiotic evolution on Earth that led to living systems; 2) the bounds 

 placed on the origin of life by the physical and chemical conditions associated 

 with the formation and early evolution of planets; 3) geochemically plausible 

 pathways by which prebiotic chemical systems became living systems; 4) the 

 characteristics of the common ancestor of extant life and the conditions that 

 prevailed in its environment; 5) the presence of extant or extinct life on Mars; 

 6) the influence of geological processes (such as tectonism) and astrophysical 

 processes (including asteroid impacts) on the evolution of life; and 7) the proba- 

 bility that technological civilizations exist nearby in the galaxy. The scientific goals 

 and objectives and the strategies for achievement described below are consistent 

 with those given in the draft report of the Space Science Board's Committee on 

 Planetary Biology and Chemical Evolution (1). 



The Cosmic Evolution of the Biogenic Compounds 



The primary research goal in this program component is to determine the 

 pathway followed by the principal biogenic elements (C, H, N, O, P, S) and their 

 compounds, including water, from their birth in stars to their incorporation and 

 final transformations in the asteroidal and cometary building blocks of planetary 

 bodies. Six stages along the pathway of cosmic evolution have been defined for 

 study: 1) nucleosynthesis and ejection of biogenic elements and compounds into 

 the interstellar medium (ISM), 2) chemical evolution in the ISM, 3) protostellar 

 collapse, 4) chemical evolution in the protosolar nebula, 5) growth of planetesimals 

 from dust, and 6) accumulation and thermal processing of planetoids (2). 



The possibility of determining a cosmic history for the biogenic elements and 

 compounds is becoming a reality as exciting discoveries emerge from new 

 astronomical observations of the ISM, increased theoretical understanding of 

 processes occurring in the ISM and during formation of the solar system, and 

 detailed analyses of meteorites, comets, and cosmic dust (2,3). 



Organic compounds containing up to 11 atoms of H, C, and N have been 

 detected in the gas phase of interstellar clouds along with many simpler 

 compounds that, in the context of the chemistry of early Earth, have been 

 attributed as building blocks in the prebiotic synthesis of amino acids and 

 nucleotides. Organic matter also appears to be a major component of interstellar 

 dust. And around carbon stars are seen hydrocarbons and tine-grained carbo- 

 naceous dust presumably formed from elemental species flowing out of the 

 interiors. Along with water in the forms of ice and gas, organic compounds are 

 widespread in the galaxy in interstellar and circumstellar regions, thus supporting 

 the view that the chemistry of the cosmos is largely organic chemistry. Many 

 tantalizing questions are raised bv these astronomical observations. For example, 

 what level of molecular complexity can be attained in circumstellar and interstellar 

 K chemistry? Arc amino acids or nucleic acid bases formed in the ISM? 



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