The gas planets are Jupiter, Saturn, Uranus and Neptune. These planets contain mostly gases, such as hydrogen and helium, and have a relatively small amount of rocky land. These planets have an complex atmospheres and in many cases, giant storms. these planets probably started out as icy rocks, and are able to collect hydrogen and helium. Jupiter and Saturn probably had bigger starting rocks, making it easier to collect these gases. Uranus and Neptune have bigger orbits and are smaller, it was harder for them to collect hydrogen and helium as efficiently as Jupiter and Saturn. This likely explains why they are smaller than those two planets. Their atmospheres are more “polluted” with heavier elements such as methane and ammonia because they are so much smaller.