The distinction between the inner planets and the outer planets in our solar system is primarily based on their composition, location, and size. The inner planets, which include Mercury, Venus, Earth, and Mars, are situated closer to the Sun. They are predominantly rocky and have solid surfaces, which is why they are often referred to as terrestrial planets. In contrast, the outer planets—Jupiter, Saturn, Uranus, and Neptune—are located further from the Sun and are classified as gas giants (or ice giants in the case of Uranus and Neptune). These planets are much larger than the inner planets and do not have solid surfaces like the terrestrial planets.
Another significant feature that separates these two groups is the asteroid belt, which lies between Mars and Jupiter. This region is densely populated with rocky and metallic bodies, acting as a natural boundary that distinguishes the inner rocky planets from the outer gas giants. The composition and atmospheric characteristics of these two classes of planets highlight the fundamental differences that stem from their formation and location in the solar system. Overall, the inner planets are smaller, rocky, and closer to the Sun, while the outer planets are larger, gaseous, and farther away.