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 .

The magnetic fields of Uranus and Neptune: Methods and models

“…It has recently been suggested that the Earth's conducting solid inner core may play a significant role in the dynamics of the fluid outer core and the generation of the geomagnetic field. In studies of an aw-like dynamo, Holierbach and Jones [1993] found that chaotic oscillations of the field gen- [Hubbard, 1981[Hubbard, , 1984 suggests that a rocky core would be solid, but even if iron has differentiated to form a highly conducting solid inner core, this would probably be too small compared with the dynamo region to be important. If a large solid conducting inner core is required to stabilize the magnetic field, then the reversal explanation for the fields of Uranus and Neptune could be partially correct, as they could be varying chaotically with no strongly preferred orientation.…”

“…This simple relation would be invalidated by significant compositional convection [Gubbins, 1977], thought to be important in driving the Earth's dynamo [Gubbins et al, 1979]. In Uranus and Neptune, Lindemann's law [Hubbard, 1981] suggests that the dynamo region is fully liquid, whilst a Fe/Mg silicate core is fully solid (although a multiple component system may have a lower melting point). With no obvious process to drive compositional convection, we assume the dynamos are thermally driven, so that equation (17) is valid.…”

Deep Convection in the Interior of Major Planets: A Review

“…Standard models for the interior (e.g. Hubbard 1981;Stevenson 1982;Hubbard and Marley 1989;Chabrier et al . 1992) show that only a few tens of per cent of the planetary radius is occupied by a solid core, which is immediately surrounded by the liquid metallic hydrogen layer.…”