Final answer:
The planets in Earth's solar system are composed of matter that originally formed from a massive cloud of gas and dust. The inner terrestrial planets have metal-rich, rocky compositions, whereas the outer gas giants are mostly hydrogen and helium.
Step-by-step explanation:
Planets in Earth's solar system are composed of various forms of matter that condensed from an enormous cloud of gas and dust about 4.5 billion years ago alongside the formation of the Sun. Composition differences arise from the location where these objects formed. The inner planets, known as terrestrial planets, have a metal-rich composition, comprising predominantly rocky materials.
In contrast, the outer gas giant planets—Jupiter and Saturn—are composed mainly of hydrogen and helium, reflecting the primordial matter from which the solar system originated. Other objects, such as icy comets in the Oort cloud and Kuiper belt or rocky and carbon-rich asteroids, show the diversity of materials present in the solar system.