What are Asteroids and Comets Made Of?
There are several different types of asteroid classification systems in use, making classification and referencing somewhat confusing, even to astronomers. A basic outline common to all the systems includes three categories – carbonaceous, known as the C-type, making up 85% of known asteroids, silicaceous or stony, the S-type, making up 17% of known asteroids, and metallic, called the L-type or X-type, making up the remainder at 8% of known asteroids. These types are usually broken down into various subdivisions based on spectral classification, albedo, and guesses about their composition. Some special categorization types, such as the Q, R, and V types, are so rare that they are represented by only a single asteroid. As of 4 June, 2007, 376,537 asteroids and minor planets have been registered, with a discovery rate of approximately 5,000 new bodies per month. It is estimated that there are between 1.1 and 1.9 million asteroids with a diameter of greater than 1 km in the solar system,
