Asteroid Types

The majority of asteroids fall into these broad categories:

• S-type (silicaceous): Accounts for about 17 percent of known asteroids. Relatively bright with an albedo of 0.10-0.22. Composition is metallic iron mixed with iron- and magnesium-silicates. S-type asteroids dominate the inner asteroid belt..
  
  
• M-type (metallic): Relatively bright with an albedo of 0.10- 0.18. Composition is apparently dominated by metallic iron. M-type asteroids inhabit the main belt's middle region.
  
  
• C-type (carbonaceous): Includes more than 75 percent of known asteroids. Very dark with an albedo of 0.03-0.09. Composition is thought to be similar to the Sun, depleted in hydrogen, helium, and other volatiles. C-type asteroids inhabit the main belt's outer regions.
  
  
• D-type: low albedo, reddish