Constraints on the origin and interior structure of the major planets

Abstract
From fitting models to the external gravity field of the major planets, Uranus, Neptune, Jupiter and Saturn, we find that certain interior characteristics may be common to all four. For Uranus and Neptune, a model with a central iron-silicate core of about 4 M E ( M E = mass of Earth), an ‘ice’ layer of H 2 O, CH 4 and NH 3 in solar proportions of ca . 10 M E , and an H 2 -He atmosphere of ca . M E -2M E gives a good fit to available constraints, including heat flow measurements. Models of Jupiter and Saturn have cores very similar to those of Uranus and Neptune; the H 2 -He layer, however, is much more extensive. Modes of origin consistent with these features are discussed. Such models predict a considerable enrichment of deuterium relative to primordial solar abundances in Uranus and Neptune. Such enrichment is not observed in Uranus; implications for interior structure and origin are discussed. Abundances of other elements are discussed in terms of interior structure and origin. We review various problems related to observed heat flow values and constraints on the dimensionless tidal quality factor, Q .

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