No, not all planets and asteroids are made primarily of rock or minerals. The composition of planets and asteroids can vary significantly depending on their formation and location in the solar system.
Terrestrial Planets: Mercury, Venus, Earth, and Mars are known as the terrestrial planets. They are composed mainly of rock and metal. The innermost part, the core, is primarily made up of iron and nickel, while the outer layers consist of various minerals and rocks.
Gas Giants: Jupiter and Saturn are gas giants composed mostly of hydrogen and helium. These planets have a relatively small solid core, but the majority of their mass is in the form of thick atmospheres of gas.
Ice Giants: Uranus and Neptune are classified as ice giants. Although they have a similar structure to the gas giants, their atmospheres contain a higher proportion of "ices" such as water, ammonia, and methane. These ices make up a significant portion of their composition.
Dwarf Planets and Asteroids: Dwarf planets like Pluto, Eris, and Ceres, as well as asteroids, have diverse compositions. While some are rocky bodies similar to the terrestrial planets, others can be composed primarily of ice, carbonaceous materials, or a combination of both.
Therefore, the composition of planets and asteroids can include a range of materials, including rock, metal, ice, and various compounds, depending on their formation and location in the solar system.