Planetary structure refers to the internal composition and layers of a planet. Most planets, including Earth, have a core, mantle, and crust. The core is typically made of metals like iron and nickel, while the mantle consists of silicate rocks. The crust is the outermost layer, where we find land and oceans. Different planets have varying structures based on their size and distance from the Sun. For example, gas giants like Jupiter and Saturn lack a solid surface and have thick atmospheres, while terrestrial planets like Mars and Venus have solid surfaces with rocky compositions.