It might seem as though the planets Korean haphazardly through space, but there is precision to their movements and the source of that precision is the sun. Planets, moons, comets, meteors, meteorites, and asteroids form our solar system, so named because all nine planets orbit the sun. It is gravity that keeps the planets in orbit. If not for the gravitational pull of the sun, the planets would fly off into space. Eight of the planets revolve and rotate around the sun in an amazingly similar way. They have orbits on the same plane in the solar system, which is called the plane of the ecliptic. The exception is Pluto, which is inclined at a 16-degree angle to the ecliptic. The nine planets in our solar system are divided into two groups, the terrestrial planets, the four innermost: Mercury, Venus, Earth, and Mars all have thin atmospheres and are also comparatively small. The terrestrial planets are separated from the outer planets by a vast expanse of space. In this space is the asteroid belt, containing what scientists believe are the remnants of a planet that never formed. Beyond that lie the Jovian planets: Jupiter, Saturn, Uranus, and Neptune, planets that have a solid rocky core and atmospheres of light gases such as hydrogen. The exception once again is Pluto, largely made of ice and containing methane and ammonia.