Here's why:
* Giant Gas Planets: Jupiter, Saturn, Uranus, and Neptune are classified as giant gas planets. These planets are primarily composed of hydrogen and helium, with trace amounts of other elements.
* Abundance: Hydrogen is the most abundant element in the universe, making it a logical component of planetary formation.
* Low Density: The outer planets have significantly lower densities than the inner, rocky planets. This low density is due to the abundance of light elements like hydrogen and helium.
While hydrogen is the most prevalent, helium is also a significant component of the outer planets' composition.
