Interiors of the giant planets: Recent advances

The broad features of the interiors of the giant planets have been elucidated over the last few years with considerable success. The main new results described in this paper are based on improved equations of state and better observational data. In addition an important factor is the better understanding of the origin of the magnetic fields of these planets. The new experimental evidence that the molecular to metallic transition in hydrogen takes place near 2 Mb rather than near 3 Mb affects only slightly the current models of Jupiter but a more radical change has to be noted for the model of Saturn. Magnetic field and luminosity data indicate that in this planet the metallic H-He layer is actually split into an inhomogeneous upper layer and a He-rich lower layer. The presence of a “metallically” conducting H 2 layer on both these planets may play a role in explaining certain features of their magnetic fields. The recent three-layer model of Uranus accounts better for various observational constraints than the previous models in spite of the uncertainty about the planet's rotation period. The model also permits to interpret the Uranian magnetic field in terms of a thermally driven hydromagnetic dynamo in the planet's mostly liquid and metallic core. The models of the interior of Neptune are still rather uncertain. The presence of a strong source of internal heat on this planet seems to cast doubt on the, so far, negative evidence of its magnetic field.