246 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



is not necessarily lichens themselves that we observe in the dark-green 

 areas of Mars. 



Eather, we wish to emphasize here that the severe climate on Mars 

 does not exclude the possibility of the maintenance of life there. In- 

 deed, observations by W. M. Sinton strongly imply that an infrared 

 absorption band characteristic of many organic compounds is present 

 in tlie Martian spectrum, which strengthens the belief in some form 

 of vegetation on that planet. 



Because Mars lacks oxygen, most astronomers agree that we should 

 not expect to find a high form of life there, and I personally believe 

 this conclusion is probably right. But there is the unlikely possibility 

 that intelligent beings might have existed, or still survive, on Mars. 

 This view does not need the support of the canals, whose interpretation 

 has aroused much controversy. But since Mars' gravity is smaller than 

 the earth's, it was easier for hydrogen to dissipate, and biological 

 evolution could have started earlier on the red planet than here. It is 

 not inconceivable that intelligent beings emerged on Mars millions of 

 years ago. One might object that the rate of evolution would be slower 

 because chemical reactions would occur less rapidly at the low Martian 

 temperature. On the other hand, the development of the human brain 

 may have been completed during the glacial ages here on earth. 



The other neighbor of the earth is Venus. Carbon dioxide is 

 abundant in its atmosphere, and water vapor has recently been estab- 

 lished by John Strong, but oxygen has never been detected. There are 

 extensive clouds that prevent us from seeing the planet's actual sur- 

 face, and we can only measure the composition of the upper atmos- 

 phere. The clouds themselves probably consist of water droplets or 

 ice particles. 



Microwave observations of Venus by C. H. Mayer and his coworkers 

 yield a temperature of more than 300° C. As Carl Sagan has pointed 

 out, the high temperature of the planet is consistent with an abundance 

 of carbon dioxide and water vapor below the clouds. Both these sub- 

 stances produce a very efficient greenhouse effect, letting visible sun- 

 light pass through but preventing infrared radiation from going out. 

 Hence Venus' surface temperature probably reaches such a high value 

 that life is impossible there. 



The existence of life on other bodies in our solar system cannot be 

 categorically denied. However, because of their chemically reducing 

 atmospheres and low temperatures (or very high, for Mercury's sunlit 

 side) , life must be very primitive, if present at all. 



Elsewhere in the universe, the fundamental problem is the existence 

 of planets. Are stars always accompanied by some smaller bodies? 

 We don't have a definite answer, because of observational difficulties. 

 No earthbound telescope could detect a planet of Jupiter's size even if 



