The inner planets, which include Mercury, Venus, Earth, and Mars, are primarily composed of rock and metal. Unlike the gas giants of the outer solar system, these terrestrial planets have solid surfaces and are characterized by their density and composition.
Mercury, being the closest planet to the Sun, is made mostly of a large metallic core, surrounded by a silicate mantle. Its surface is heavily cratered, similar to the Moon, and is composed mainly of iron, making it one of the densest planets in our solar system.
Venus has a rocky composition similar to Earth, with a thick atmosphere primarily made of carbon dioxide. Its surface features include volcanic plains, mountains, and highland regions, all indicating a history of geological activity.
Earth, our home planet, has a diverse composition with a crust made of various minerals, a mantle rich in silicate rocks, and a substantial iron-nickel core. This unique composition is vital for maintaining life, including a stable climate and the presence of liquid water.
Finally, Mars has surface features that suggest a past existence of water, and its composition includes iron oxide, which gives it its characteristic red color. Mars has a thin atmosphere and a core that is likely partially liquid iron.
In summary, the inner planets are mainly made up of rocks and metals, giving them solid surfaces and the ability to support various geological processes.