322 FROM NEBULA TO NEBULA 



long ago to have prompted the thought that the oceans 

 may be normally frozen over, in which state they can as 

 easily carry surface markings as the most rigid land, and 

 more regular ones, besides. 



It would be an error to jump to the conclusion that 

 Mars' oceans must be frozen solid, for decidedly they 

 are not. For one thing, the planet could not rotate un- 

 less they were mobile, as I have previously shown; and, 

 for another, the gravistatic heat generated by the planet 

 is probably sufficient to prevent total congelation. Nor 

 should we fail to bear in mind, that the water at the bot- 

 tom of a deep ocean cannot freeze, because of its density 

 there being constantly maintained above that required 

 for freezing. 



That Mars' gravistatic heat is by no means a negli- 

 bible quantity maybe proved by a simple calculation. 

 Mars' superficial gravity being .38, one would have to 

 descend toward his center about 150 feet for each degree 

 of increase in temperature, yielding a maximum theoreti- 

 cal temperature at that point of about 40,000 degrees, or 

 an average of 20,000 for the whole mass. This is a much 

 lower temperature than our earth theoretically generates 

 and may seem insufficient until we call to mind that Mars ' 

 rarer atmosphere and lesser gravity both operate to 

 greatly lower the freezing point of the water, and that 

 ice is a bad conductor of heat as compared with convec- 

 tion currents in a purely fluid sea. 



The excessive external cold must evince itself some- 

 how, and this it does by freezing a thick crust over a 

 major portion of the ocean surface. Nevertheless, even 

 such a surface may experience seasonal changes, and this 

 is the real key to the whole mystery. It remains for us 

 now only to reason by natural steps just what would take 

 place under such conditions. 



Going toward our own north pole we come eventually 

 to a parallel of latitude of perpetual frost. In the case 

 of Mars this critical parallel is nearer the equator than 

 it is with us. During the warm season the ice-crust 

 thaws to the depth of a very few feet, but not entirely 

 through, except, perhaps, very late in the season, and 



