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asteroid belt which could sample and return materials to Earth is 

 important in our attempt to elucidate the history of the early 

 solar system and, hence, to the origins of life. 



Evidence bearing on the problem of the chemical setting for 

 prebiotic synthesis may yet be forthcoming from comparative 

 planetology. The information derived from the knowledge of our 

 sister planets will provide constraints for the origin and develop- 

 ment of our Earth. 



The colors on Jupiter have long been thought to indicate the 

 presence of organic chemical synthesis. Since the highly reducing 

 atmosphere of Jupiter is consistent with some models of the Earth's 

 early atmosphere, Jupiter may well represent a model for primitive 

 Earth's chemistry. It is becoming increasingly evident that we are 

 going to have to go there to find out. The Galileo Project will make 

 a first step in this direction, but it is clear that more sophisticated 

 explorations are required. 



In the same vein, Titan, despite its low temperature, remains 

 important because of its methane/nitrogen atmosphere, its red 

 color, and the variety of evidence suggesting the presence of a photo- 

 chemical smog. Because chemistry is taking place in this primitive 

 reducing atmosphere today, and the products of these reactions are 

 believed to be accumulating on the satellite's surface, a well- 

 preserved record of carbon cosmochemistry undoubtedly exists. 

 Thus, preliminary explorations of this environment are in order. 



Within the context of a totally different planetary environment, 

 there is still much to be learned from Mars after Viking. For exam- 

 ple, judging from the ages deduced for some parts of the surface 

 from densities of impact craters, there should be very old (older than 

 4 billion years) rocks on Mars. These rocks should presumably tell us 

 whether or not Mars ever had a strongly reducing atmosphere. 



In addition, detailed surface analysis of Mars may yet provide 

 information about organic matter in protected environments, and 

 information on the ages of various strata would be fundamental in 

 understanding the epochs of liquid water. Finally, the mineralogy 

 would help to answer two important questions. First, are the "miss- 

 ing volatiles" tied up in the form of carbonates, nitrites, nitrates, and 

 sulfates? And second, laboratory studies using iron-rich clays appear 

 to satisfactorily explain the results of the Viking experiments. Are 

 these clays present, and if present what is their nature? Thus, we are 



