Berger: Radiation Effects in Space 



485 



In another experiment, methane, water, and ammonia were condensed to a 

 solid icy mixture and irradiated with 12 Mev protons.''^ These conditions 

 approximate the environment thought to exist on comet heads. Analysis of 

 the reaction mixture indicated the presence of urea, acetamide, and acetone. 

 The mechanism of this reaction proceeds presumably through a free radical 

 stage. Either the radicals react with each other in the cold when radical 

 concentrations become too high, or reaction takes place when the reaction site 

 warms up to a higher temperature. Similar reactions may not only occur on 

 comets and icy meteors, but also on the colder outer planets of the solar system 

 and their satellites. 



Based upon astronomical, chemical, and physical observations, it is clear 

 that not all reactions apply to the same body in space; rather certain reac- 

 tions will not occur in some instances but play a major role in others. There- 

 fore, it is essential to consider carefully the environment of the object in 



NUCLEIC ACID STRUCTURE 



OH OH °V/°" 



-0 P^— — CH-CH-CH— — ^^P — — CH-CH — > — 



2 



ADENINE N 



/ \ 



CM2 



H "CH^ 



/ \ 



^ I 



THYMINE 



H. 



H 



/•^-c-^° 



/ \ 



CH» O 



N C 



GUANINE 



/C^^/'^N^" 



"^ ^c^ ^c- 



CYTOSINE 



H >• ' O'' Nh2 





CH, 



\ / 



-0— ^P.— 0-CH,-CH — CH_o — P — CHi-CH-CH— 0-^--0 — 



OH 



0' OH 



Figure 3. 



OH ^0 



space before assigning which reactions may predominate. Glasel bombarded 

 solid D2O with electrons and observed the liberation of considerable amounts 

 of D2 .^^ Because the bond energy of the D — O bond is higher than that of the 

 C — H bond in organic compounds, it is to be expected that over periods of 

 time unshielded organic compounds will be destroyed in space. Therefore, 

 organic material initially produced on cosmic grains will not remain intact. 

 Similar destructive radiation effects will occur elsewhere; it is only there, where 

 shielding from damaging radiation comes into play, that organic compounds 

 will be available for further reactions. 



If I may speculate a little, it may very well be that initially radiation may 

 have been the agent which at least in part built up molecules to such systems, 

 which finally were able to handle in a controlled manner radiation or rather 

 light quanta. The first such successful system to use radiation energy for the 

 synthesis of organic compounds was the beginning of photosynthesis. 



In conclusion, let me say that with the aid of radiation as a form of energy, 

 one can synthesize chemical species which are the building blocks of proteins, 

 nucleic acids and other important biological compounds. 



