The outer planets of our solar system are composed of

Gas giants are made up primarily of hydrogen and helium the same elements that make up most of the sun

Hydrogen and helium (gasses).

From left to right, the outer planets are Jupiter, Saturn, Uranus, and Neptune. The gas giants are made up primarily of hydrogen and helium, the same elements that make up most of the Sun. Astronomers think that hydrogen and helium gases comprised much of the solar system when it first formed.