Question

Are not outer planets made up of methane gas?

Answer 1

Jupiter, Saturn, Uranus and Neptune collectively make up the group known as the jovian planets or outer planets. The general structures of the outer planets are opposite those of the terrestrial planets. Rather than having thin atmospheres around relatively large rocky bodies, the outer 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.
So yes they do contain methane gas but it is not the predominant gas.