LIFE IN THE UNIVERSE — HUANG 245 



All these results suggest that complex compounds of carbon can 

 be formed easily from inorganic substances when conditions are suit- 

 able. We may not be seriously wrong if we assume that life every- 

 where in the universe depends on carbon compounds. 



The question of life elsewhere in the solar system is no longer as 

 speculative as it was even a decade ago, and in 10 years we may have 

 definite proof concerning the present existence of living beings on other 

 planets. But if no life is found, it does not prove that none ever 

 appeared — such proof requires actual excavation of a planet's surface, 

 which may take a few decades to achieve. 



Mars is most frequently mentioned as a possible former or present 

 abode of life. Despite its small gravitational attraction (with only 10 

 percent of the earth's mass), its surface gravity is 37 percent of ours 

 and it retains an atmosphere. There is no hydrogen or helium ; none 

 is expected. Spectroscopic observations show carbon dioxide is pres- 

 ent, but the search for oxygen has been negative. Mars' atmosphere 

 contains less than 1/1,000 as much oxygen as the earth's, yet there is 

 doubtless much nitrogen. 



Although spectroscopic observations have failed to detect water 

 vapor on Mars, its presence may be indicated by the seasonal variations 

 of the polar caps. However, the physical nature of the polar caps is 

 still debatable. Some observers consider them to be made of ice, 

 but others, like C. C. Kiess and his collaborators (Sky and Telescope, 

 June 1960, p. 469), explain the caps as solid nitrogen tetroxide. 



The temperature of Mars' equatorial region can reach a maximum 

 of about 30° C, but in general is lower than on earth. Since 

 not much water exists in the Martian atmosphere to keep heat from 

 radiating away into space at night, the temperature probably reaches 

 as low as — 100° C. Whether life can be maintained under these con- 

 ditions has interested astronomers for a long time. 



Dark green areas in the equatorial regions suggest that plant life of 

 some form is present on Mars. The color and shade of these markings 

 change with the seasons in a way that indicates the growth and decay 

 of vegetation (darker in spring and lighter in autumn). Because of 

 the very severe climate, no higher terrestrial plants could survive. 

 However, special kinds, such as lichens, might live. A lichen is a 

 symbiotic plant composed of two different organisms: fungus and 

 alga. These can flourish together under conditions that would be 

 fatal if either had to meet them alone. 



The fungus, which does not perform photosynthesis, derives food 

 from the alga, which does. But the fungus helps maintain the water 

 supply necessary for growth of the alga. Consequently, this symbiotic 

 plant occurs all over the earth, enduring many kinds of extreme 

 climate, from burning deserts to freezing mountaintops. However, it 



