<P> An asteroid spectral type is assigned to asteroids based on their emission spectrum, color, and sometimes albedo . These types are thought to correspond to an asteroid's surface composition . For small bodies that are not internally differentiated, the surface and internal compositions are presumably similar, while large bodies such as Ceres and Vesta are known to have internal structure . Over the years, there has been a number of surveys that resulted in a set of different taxonomic systems such as the Tholen, SMASS and Bus--DeMeo classification . </P> <P> The present - day classification was initiated by Clark R. Chapman, David Morrison, and Ben Zellner in 1973 with three categories: C for dark carbonaceous objects, S for stony (silicaceous) objects, and U for those that did not fit into either C or S . This classification has since been expanded and clarified . </P>

How many different types of asteroids are there