Giant Planets and their Satellites: What are the Relationships Between Their Properties and How They Formed?

The giant planet region in our solar system appears to be bounded inside by the limit of water condensation, suggesting that the most abundant astrophysical condensate plays an important role in giant planet formation. Indeed, Jupiter and Saturn exhibit evidence for rock and/or ice cores or central concentrations that probably accumulated first, acting as nuclei for subsequent gas accumulation. This is a "planetary" accumulation process, distinct from the stellar formation process, even though most of Jupiter has a similar composition to the primordial Sun. Uranus and Neptune are more complicated and imperfectly understood, but appear to exhibit evidence of an important role for giant impacts in their structure and evolution. Despite some interesting systematics among the four major planets and their satellites, no simple picture emerges for the temperature structure of the solar nebula from observations alone. However, it seems likely that Jupiter is the key to our planetary system and a similar planet could be expected for other systems. It is further argued that we should expect a gradual transition from solar nebula dominance to interstellar dominance in the gas phase chemistry of the source material in the outer solar system because of the inefficiency of diffusion in the solar nebula. There may be evidence for this in cornets. Similar effects to this may have occurred in the disks that formed around Jupiter and Saturn during their accretions; this may show up in satellite systematics. However, each satellite system is distinctive, preventing general conclusions.