Interiors of the Uranus and Neptune

Uranus and Neptune are similar to Jupiter and Saturn in that they have large rocky cores and are primarily hydrogen and helium. However, they are not the same in all respects. Their outer layers are hydrogen molecules H₂, their middle layers are slushy material ( liquid water, methane, and ammonia), and their inner regions are composed of rocky type material (the seed from the planet formation process). Because of their lower masses compared to Jupiter and Saturn, the pressures in their interiors does not get as large and metallic liquid hydrogen does not form.

A comparison of the interiors of Jupiter and Saturn to those of Uranus and Neptune is shown below.

Again, how do we determine these general properties?

• density ---> made of primarily light stuff ---> hydrogen and helium
• seismology ---> no
• magnetic fields ---> yes ---> molten, conducting layer is needed--the ionized ammonia in the mantle forms a nice conductor for this purpose
• nonspherical shapes (flattening due to rapid rotation) ---> interior structure

An interesting sidelight is that again Neptune radiates more energy than it receives from the Sun, roughly 2.7 times as much energy. Interestingly, however, Uranus does not exhibit this behavior. It is not clear why two such similar planets do not behave the same.