The Asteroid Belt-Rubble of the Solar System:

There is a gap of 547 million kilometers, between the orbits of Mars and Jupiter.  In this gap are thousands of  bodies made of rock and metal, ranging in size from mere specks of dust to hundreds of kilometers. These are called asteroids, and are believed to represent original solar material which failed to bind together to form a planet. The first asteroid was discovered  in  1801  by Giuseppi Piazzi, who named  it Ceres. It is 960 km across. The number of asteroids known now runs into thousands. Most asteroids are irregular in shape. They reflect varying amounts of  light as  they travel through space. Their shapes suggest that they may be the product of a collision  

or an explosion. Thousands of fragments of asteroids enter the Earth's atmosphere every year, producing a streak of  light across the sky. This streak of  light shooting across the sky is called a meteor. Of  the objects that enter the Earth's  atmosphere, mgny are of  the size of  a grain of  sand or a pebble and  they are destroyed  in  flight. The objects that are large enough to survive the flight and hit  the Earth's surface are called meteorites. A meteorite is like a piece of  the Solar System right in our laboratory. The chemical analysls of meteorites provides us vital information about the Solar System. 

Thus far, we have described some characteristics of  terrestrial planets, except the Earth and its satellite Moon. You will now study some features of  the Jovian planets and the comets.