There are eight official planets in our solar system. Pluto was once considered to be the ninth planet, but on August 24, 2006, it was downgraded to be a dwarf planet by the IAU. The planets are separated into two groups, the inner and the outer planets.

      The inner planets, the ones that orbit closest to the Sun, are Mercury, Venus, Earth and Mars. They are terrestrial or rocky. The outer planets are Jupiter, Saturn, Uranus and Neptune. They are much larger and gaseous.

      Between the inner and outer planets lies the Asteroid Belt, home to 4,000 named Asteroids, and most likely over 100,000 more! Beyond Pluto lies the Oort Cloud, home to perhaps a trillion comets!

     The orbits of the planets does not mark the end of our solar system. Any of the dust that is beyond them that is controlled by the Sun's gravity is considered to be part of our solar system. The Kuiper Belt contains many objects on the fringe of our solar system, including Eris, a newly discovered dwarf planet. The true end of the system is called the Heliopause. That is the point where our Sun's gravity has no effect.

      It is believed that our solar system began life as a great cloud of gas and dust about 4.5 billion years ago, which began to collapse in on itself under the force of gravity. As the cloud shrank, it started to spin and flatten out into a disk. Eventually, the center began to heat up as the particles of gas and dust smashed into each other, forming the star we know as our Sun. The rest of the material went on to form the planets, moons, asteroids, comets, and other debris that make up the solar system.