The outer planets have
no solid surface, and are much bigger. The primary gases are hydrogen and helium (like the Sun), although Uranus
and Neptune have substantial (15 Earth
mass) rock/ice cores.
This is mostly
to discuss relative sizes. Jupiter and Saturn are true gas giants; Uranus and
Neptune are more like “ice giants” (though with deep gaseous exteriors). Can
mention that it takes a core about the size of their cores to attract gas
directly from the solar nebula (which needs to be defined).
