The Sun's family consists of eight planets with at least 162 moons. There are four inner planets: Mercury, Venus, Earth, and Mars. These planets are small and rocky. There are four outer planets: Jupiter, Saturn, Uranus, and Neptune. These planets are large and composed of gases. They are often called the gas giants. There are also three dwarf planets: Ceres, Pluto, and Eris. They have a total of four moons. Together these objects exist on a plane that is over 10 trillion km in diameter.
The inner and order outer planets are separated by the Main Asteroid Belt. The belt lies between Mars and Jupiter and is composed of hundreds of thousands of small rocky bodies. These are often called planetoids.
Beyond the orbit of Neptune is another region called the Kuiper Belt. It is a disk-shaped region containing many small icy bodies. Many comets come from this belt. Far beyond the Kuiper Belt is another vast cloud of comets called the Oort Cloud.
IDENTIFY: Which planets are known as the gas giants?
Planet Pathways
Ancient peoples observed that the planets changed their positions among the stars. The planets seemed to wander in the sky. The word planet comes from a Greek word meaning "wanderer"