Anders: Origin of Carbonaceous Chondrites 



523 



there will be a permafrost zone,* and the ice from this zone will evaporate at a 

 rate determined by its vapor pressure (Watson et al., 1961). The vapor pres- 

 sure depends upon the temperature, which in turn depends on the distance from 

 the sun. For a body with 100-km. radius, with an initial water content of 10%, 

 these times are indicated in table 4. 



Unfortunately, this water zone is located in a dark, underground region, 

 where photosynthetic organisms could not grow or reproduce. To support 



4000 



0.00 



Relative Fractional Volume 



Figure 6. Temperature distribution of asteroids heated by radioactivit}- or some other 

 uniformly distributed internal heat source. The 2 solid curves are calculated for different 

 heating rates, assuming heat transport by conduction only; the daslied curve includes an allow- 

 ance for convective heat transport as well. In all 3 cases, some 5 per cent of the body will 

 find itself in the temiierature range 273° to ^400° K., in which liquid water can exist. Melt- 

 ing points of important meteorite minerals are indicated by horizontal lines. (Reproduced 

 from fish el al., 1960, with permission of the editor. Copyright, 1960 by the University of 

 Chicago.) 



life, some source of free energy must be available. Sunlight could provide this 

 free energy indirectly, if some mechanism existed for bringing photosynthetic 

 products from the surface to the interior. It is hard to see how this might be 

 accomplished without a liquid vehicle. Hence, the principal remaining possi- 

 bility is to derive the free energy from a local source, as first suggested by Sagan 

 (1961). A nonequilibrium assemblage of minerals might provide such a source. 



* This permafrost zone can serve to retain an "internal atmosphere" within the meteorite 

 parent bodN', and mav have played a role in the retention of noble gases (DuFresne and Anders, 

 1962a,b). 



