Final answer:
Jovian planets like Jupiter and Saturn have a unique composition, primarily consisting of gases and ices. They acquired these compositions during their formation, capturing gases like hydrogen and helium. Furthermore, they also possess denser cores made of rock, metal, and ice.
Step-by-step explanation:
The common usage of gas, ice, and rock does not hold on Jovian planets like Jupiter and Saturn because of their unique composition and formation process. Jovian planets are primarily composed of gases such as hydrogen and helium, as well as ices like water, methane, and ammonia. These elements are abundant in the outer solar system where temperatures are cooler.
The collapse of gas from the nebula onto the cores of Jovian planets explains their hydrogen-rich composition. Jupiter and Saturn captured more gas during their formation, resulting in their cosmic compositions. On the other hand, Uranus and Neptune captured less gas, leading to their compositions dominated by icy and rocky building blocks.
Additionally, Jovian planets have cores made of heavier rock, metal, and ice. The denser cores are inferred from gravity studies and are hidden beneath the visible atmospheres of these planets.