Types of Asteroids

Asteroids are generally classified in 2 different ways:

1. Composition
2. Distance from the Sun 

Composition

· C-type: Most common, contain lots of carbon, extremely dark (Itokawa)

· S-type: Made from compounds of silicon (433 Eros)

· M-type: Contain metal, moderately bright (16 Psyche)

Distance from the Sun

1. Amors - Earth approaching NEA's with orbits exterior to Earth but interior to Mars.
   a > 1.0 AU, 1.017 AU < q < 1.3 AU
2. Apollos - Earth-crossing NEA's with semi-major axes larger than Earth's.
   a >1 .0 AU, q < 1.017AU
3. Atens - Earth-crossing NEA's whose semi-major axes are smaller than Earth's
   a <1 .0 AU, Q > 0.983 AU
4. Atrias- NEA's whose orbits are contained entirely within the orbit of Earth
   a < 1.0 AU, Q < 0.983 AU 

a = Semi-Major Axis

q = Perihelion

Q = Aphelion