SECRETARY'S REPORT 161 



Cytherean clouds and atmosphere, including semi-infinite, purely ab- 

 sorbing atmospheres in radiative or convective equilibrium, and 

 multiple-scattering cloud layers with a range of single-scattering al- 

 bedos, again in radiative or convective equilibrium. Calculations in 

 another paper show that the microwave phase effect can be explained 

 in terms of the thermal and electrical properties of certain geochem- 

 ically abundant materials at the temperatures of Venus's surface, 

 assuming very slow planetary rotation. 



Conditions on Mars have also been studied by Dr. Sagan, who has 

 found that the wave of darkening is preferentially localized in times 

 and locales on Mars when the mean daytime temperatures in the nuclei 

 of the dark areas are above the freezing point of water. This result 

 is consistent with the hypothesis that the wave of darkening is a bio- 

 logical response to local increases in humidity and temperature. From 

 investigations of the question of nitrogen oxides on Mars, Dr. Sagan 

 and his associates find that previously published observations of Mars 

 in the infrared, visible, and ultraviolet set an upper limit to the NO2 

 abundance there of about 1 mm-atm. If there is no water on Mars, the 

 theoretical upper limit obtained from photochemical and thermo- 

 dynamic equilibrium is also 1 mm-atm. With 10 microns of precipi- 

 table water in the Martian atmosphere, the NO2 upper limit is reduced 

 by an order of magnitude. These quantities of NO2 are so small that 

 it seems unlikely that the nitrogen oxides play a significant role in 

 any observable on Mars, except possibly the blue haze. 



Life may have evolved on other planets of this or other solar systems 

 as it has on the planet earth. Dr. Sagan and his colleagues have 

 reported the laboratory synthesis of one of the key molecules impli- 

 cated in the origin of life. The molecule, adenosine triphosphate 

 (ATP), supplies most of the energy for chemical processes in all 

 terrestrial organisms. The work was performed in collaboration with 

 Cyril Ponnamperuma and Euth Mariner, at NASA's Ames Research 

 Center. The ATP was synthesized by shining ultraviolet light on a 

 solution of adenine, ribose, and a phosphorus compound. Adenine 

 and ribose have previously been synthesized in similar experiments; 

 phosphates are thought to have been present in the primitive oceans. 

 Because of the absence of ozone from the primitive atmosphere of the 

 earth, ultraviolet light is thought to have penetrated to the primitive 

 oceans. The efficiency with which ATP was produced in these experi- 

 ments suggests the possibility that the first organisms on earth ob- 

 tained most of their energy from ATP synthesized abiologically by 

 ultraviolet solar radiation, instead of from metabolically produced 

 ATP, as contemporary organisms do. 



Drs. Fred Franklin and Allan F. Cook have continued their study 



