The Solar System consists of a Sun and a system of eight planets, their moons, and other non-stellar objects. It was believed to be formed about 4.6 billion years ago from the gravitational collapse of a giant molecular cloud. The Solar System also contains a number of regions populated by smaller objects known as the asteroid belt, which lies between Mars and Jupiter, and is composed of rock and metal.
The Solar System is located within one of the outer arms of Milky Way galaxy, which contains about 200 billion stars. At the heart of the solar system is our sun. The four planets nearest it are rocky, terrestrial worlds ? Mercury, Venus, Earth and Mars. After that are four gas giants ? Jupiter, Saturn, Uranus and Neptune. There are now officially only eight planets in our solar system, Pluto no longer qualifies as a planet.