Asteroids have several general features of interest.

1) Firstly, their formation - they all represent material that was not used in the initial formation of the solar system.

2) For whatever reason - chance and position - they did not form planets, and therefore were left scattered.

3) They do not represent much material - it is thought that if they were all joined together the mass would only be that of half of our Moon!

4) Most asteroids are in a 'belt' between Mars and Jupiter.

5) Some asteroids even have their own mini moons - for instance Ida and Dactyl.