SECRETARY'S REPORT 153 



among several possible alternative primitive compositions for a proto- 

 Earth. 



Exobiology. — Ultraviolet irradiations of possible simulated primi- 

 tive terrestrial environments, which Dr. Sagan performed in coopera- 

 tion with Dr. C. Ponnamperuma, exobiology division, Ames Eesearch 

 Center, NASA, have produced nucleoside phosphates and other mole- 

 cules intimately involved in contemporary terrestrial biological proc- 

 esses. Such synthetic reactions had been predicted by Dr. Sagan in 

 1957. 



Dr. Sagan made other studies on methods for detection of extrater- 

 restrial life and on the frequency of possible advanced extraterrestrial 

 life forms. Using Mie theory and a computer program, he is continu- 

 ing a critical study of the panspermia hypothesis. 



In an experimental program performed by Dr. Sagan in coopera- 

 tion with Dr. Stanley Scher at the University of California Space 

 Sciences Laboratory,^ simulated Martian environments have been 

 inoculated with a variety of terrestrial soil types and assayed for the 

 survival of the contained terrestrial microorganisms. The preliminary 

 results indicate that all samples of terrestrial soil tested have a popula- 

 tion of microorganisms that can probably survive on Mars. This 

 conclusion emphasizes the necessity for rigorous sterilization of Mars- 

 impacting space vehicles. 



Lunar science. — The moon is now the object of intense investigation 

 by many scientists from all parts of the world. This interest is 

 stimulated, of course, by past and forthcoming lunar probes, orbiters, 

 softly landed instrumentation packages, and eventual manned 

 exploration. 



The Astrophysical Observatory is pursuing several lunar investi- 

 gations which are closely related to its other programs and for which, 

 therefore, the Observatory is peculiarly well prepared. One such 

 topic is the determination of the moon's gravitational potential from 

 analyses of the motion of bodies orbiting it. Attempts by the United 

 States to launch lunar orbiters have been unsuccessful to date, but 

 will undoubtedly meet eventual success. Dr. Kozai has completed an 

 approximate analytical study of the motion of an orbiter. He is pro- 

 ceeding with a program for numerically integrating the equations of 

 motion. 



Drs. Lautman and Colombo have shown that radiation pressure 

 significantly changes the orbit of a "balloon" spacecraft and could 

 effect a lunar capture of an initially geocentric orbit. 



The impacts of meteorites on the moon produce craters of all sizes, 

 depending upon the size and velocity of the incident body. Tlie size 

 distribution of lunar craters has been analyzed by Dr. Gerald S. 



See footnotes on p. 164. 



