| Popis: |
The presence and compositions of atmospheres on the terrestrial planets do not follow directly from condensation models which would have earth accreting near 500 K. No single mechanism yet proposed adequately accounts for the abundances of noble gases and carbon and nitrogen in the atmospheres. We show that the composition of clathrates forming at low temperatures in cold regions of the nebula can be predicted. Addition of about 1 ppm clathrate material to the earth can explain observed abundances of Ar, Kr, and Xe. Condensation and adsorption processes occurring at 400-500 K are necessary to explain the observed abundances of Ne, H2O, C, and N. Possible sources of clathrates could be cometary bodies formed in the outer solar system. |
