Terrestrial planets are the rocky planets in our solar system, which include Mercury, Venus, Earth, and Mars. These planets are characterized by their solid surfaces, composed mainly of rock and metal. They are closer to the Sun compared to the gas giants, and they have relatively small sizes and higher densities. Each terrestrial planet has unique features, such as Earth's abundant water and Mars's red surface. Unlike the gas giants, terrestrial planets have thin atmospheres, with Venus having a thick, toxic atmosphere and Mercury having almost none. These planets also have various geological features, including mountains, valleys, and craters. Studying terrestrial planets helps scientists understand the formation of our solar system and the potential for life beyond Earth.