ENRICHMENT OF CO OVER N-2, BY THEIR TRAPPING IN AMORPHOUS ICE AND IMPLICATIONS TO COMET P HALLEY/

Observations of Comet P/Halley showed a cosmic abundance ratio of carb on and oxygen but a depletion of nitrogen. We checked the composition of amorphous water ice samples deposited on a cold plate from gaseous mixtures with various CO:N-2:H2O-vapor ratios at several temperatures. From measuring the amounts of N-2 and CO which are trapped together i n the ice, we found an obvious enrichment of carbon monoxide over mole cular nitrogen. We therefore propose a possible explanation for the de pletion of N-2 in the volatile inventory of Comet P/Halley. The altern ative possibility, that intact ice-coated interstellar grains were coa gulated into cometary nuclei, is also discussed and arguments against it are brought up. (C) 1996 Academic Press, Inc.