A Tour of the Solar System

Our solar system is the Sun and everything that travels around it. Eight planets circle the Sun in paths called orbits. Mercury is closest and moves fastest; Neptune is farthest and takes about 165 Earth years for one trip around.

The four inner planets - Mercury, Venus, Earth, and Mars - are rocky worlds with solid ground. The four outer planets - Jupiter, Saturn, Uranus, and Neptune - are giant balls of gas with no solid surface to stand on. Jupiter is so big that more than a thousand Earths could fit inside it.

Between Mars and Jupiter lies a belt of asteroids, chunks of rock left over from when the planets formed. Beyond Neptune are icy worlds like Pluto, which is called a dwarf planet. Everything in the system is held together by the Sun's enormous gravity.