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Evidence for Lunar-Type Objects in the Early Solar System

Published online by Cambridge University Press:  30 March 2016

H. C. Urey
H. C. Urey*
Affiliation:
Chem. Dept., University of California, San Diego, La Jolla, Calif. 92037, U.S.A.

Extract

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Objects of the solar system, in addition to the Sun, can be classified into four groups -the planets, objects of lunar mass, smaller objects of variable mass and the comets.

If the solar proportion of gases relative to non-volatile compounds of the variety in the terrestrial planets, namely about 300 times the mass of these elements, were added to the terrestrial planets, they would have masses comparable to those of the major planets. Mercury is low in mass but has a high density, indicating that it has lost several times its mass of silicate materials relative to high density metallic iron. If this were restored and then the component of gases were added, it would also fall into the group rather naturally. Mars appears to be rather small. Uranus and Neptune have rather high densities indicating some loss of gases, probably hydrogen and helium. When we attempt to estimate the mass of primitive solar material from which the planets were evolved, we conclude that they evolved from very similar masses. Later, I shall argue that the process was a very inefficient one.

Type
Joint Discussions
Information
Highlights of Astronomy , Volume 3: Highlights of Astronomy. As presented at the XVth General Assembly of the IAU, 1973 , 1974 , pp. 475 - 481
Copyright
Copyright © Reidel 1974

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