What are the surfaces of the outer planets mostly made of

Jupiter, Saturn, Uranus and Neptune collectively make up the group known as the jovian planets. The general structures of the jovian planets are opposite those of the terrestrial planets. Rather than having thin atmospheres around relatively large rocky bodies, the jovian planets have relatively small, dense cores surrounded by massive layers of gas. Made almost entirely of hydrogen and helium, these planets do not have solid surfaces.

The outer planets are mostly made of gassy carbon dioxid with no gravity and surface which means no ground to stand on.