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1. The Pristine Nature of Comets

Published online by Cambridge University Press:  12 April 2016

A. H. Delsemme

Abstract

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Abundance considerations suggest that comets are likely to be the most pristine minor bodies in the solar system. In proportion to solar abundances, the present scanty data suggest that cometary oxygen is not depleted, whereas carbon is by a factor of 4 and hydrogen, by a factor of 2000. This implies that comets are less depleted in H, C, N, O than CI chondrites, namely 10:1 in hydrogen, 4:1 in carbon and 3:1 in oxygen. These results have been obtained by using dust-to-gas ratios in comets, to measure the relative abundance of silicon and metals to volatile material, and the spectra of atomic lines, mainly from the vacuum ultraviolet, to determine the H/O and C/O ratios of the mixture of volatile molecules.

Type
Part I. Physical Nature of Comets
Information
International Astronomical Union Colloquium , Volume 39: Comets, Asteroids, Meteorites: Interrelations, Evolution and Origins , December 1977 , pp. 3 - 13
Copyright
Copyright © A.H. Delsemme 1977

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