On the Constitutions of the Major Planets

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Abstract
The internal constitutions of the major planets are investigated on the. basis of the atomic theory of solids. The starting-point of the investigation is the theoretical pressure–density relationship for solid hydrogen at absolute zero temperature; the internal temperatures of the planets are shown to be too low to influence the densities appreciably. It is shown from the empirical mean densities that the most massive planets, Jupiter and Saturn, are predominantly hydrogen. The hydrogen content of Jupiter is about 80 per cent by mass and that of Saturn about 60 per cent by mass. The proportions of hydrogen in these planets are comparable with that in solar material. The internal density distributions in Jupiter and Saturn have been estimated on the assumption of chemical homogeneity. The proportion of heavier elements has been chosen for each planet to agree with its empirical mean density. The computed moments of inertia of the planets are close to, but definitely larger than, the empirical values. This probably means that the heavier elements are not distributed uniformly in the planets but are to some extent centrally condensed. Uranus and Neptune are about ten times as dense as hydrogen planets of the same mass, and their mean atomic weights are about four; these planets are presumably composed mainly of water, methane and ammonia. The cosmogonical significance of these results is briefly discussed.

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