The sun and the solar wind seem to do a good job of fractionating lighter materials to the outer solar system and leaving heavier materials in the inner solar system. So we end up with rocky/metallic planets in the inner solar system and the gas giants and ice giants in the outer solar system. But But why are the gas giants (Jupiter and Saturn composed mainly of Hydrogen and Helium - the lightest materials) closer to the sun than the ice giants (Uranus and Neptune composed of water, ammonia, methane, etc.)?
