All Planet Sizes

The planets vary greatly in size but can be easily sorted into two groups. During the formation of the solar system, each planet developed particular characteristics based on its distance from the Sun. Closer to the Sun, where the temperature was hot, smaller planets formed out of rocks and metals. The inner planets—Mercury, Venus, Earth, and Mars—are known as the terrestrial, or rocky, planets. Mercury and Venus do not have any moons, Earth has one moon, and Mars has two moons. Farther away from the Sun, where it was cool, larger planets formed from icy materials and gases. The outer planets—Jupiter, Saturn, Uranus, and Neptune—are known as Jovian, or gas giant, planets. The outer planets are largely made of gases and they likely have cores of molten rock. Each outer planet also has many moons.

Leftover materials that were not incorporated into planets became rocky asteroids, mostly located in the asteroid belt between Mars and Jupiter, and icy comets and Kuiper belt objects (KBOs) in the outer solar system. There are innumerable icy and rocky objects in the Kuiper belt, which lies beyond the outer planets, and in the Oort cloud at the outer edges of the solar system. Some of the larger objects are called dwarf planets—they may have layers of rock, ice, and atmosphere like the other planets but they are smaller than the terrestrial planets. Most of the dwarf planets like Pluto and Eris are located in the outer solar system.

Image: All Planet Sizes