Universe Today
Main Belt Asteroids: (which includes the majority of known asteroids which orbit within the asteroid belt between Mars and Jupiter)
Trojans: These asteroids share an orbit with a larger planet, but do not collide with it because they gather around two special places in the orbit (called the L4 and L5 Lagrangian points). There, the gravitational pull from the sun and the planet are balanced by a trojan's tendency to otherwise fly out of the orbit. The Jupiter trojans form the most significant population of trojan asteroids. It is thought that they are as numerous as the asteroids in the asteroid belt. There are Mars and Neptune trojans, and NASA announced the discovery of an Earth trojan in 2011.
Near-Earth Asteroids: These objects have orbits that pass close by that of Earth.
Atiras are NEAs whose orbits are contained entirely with the orbit of the Earth, having a distance of less than 1 AU. They are named after asteroid 163693 Atira.
Atens are Earth-crossing NEAs with semi-major axes smaller than Earth's, with a distance of less than 1 AU. They are named after asteroid 2062 Aten.
Apollos are Earth-crossing NEAs with semi-major axes larger than Earth's, with a distance of less than 1 AU. They are named after asteroid 1862 Apollo.
Amors are Earth-approaching NEAs with orbits outside of Earth's but inside of Mars' orbit. They are named after asteroid 1221 Amor.
C-type (chondrite) asteroids are most common, making up about 75 percent of known asteroids. They are very dark in appearance and probably consist of clay and silicate rocks. They are among the most ancient objects in the solar system. Their composition is thought to be similar to the Sun, but depleted in hydrogen, helium, and other volatiles. C-type asteroids mainly are in the asteroid belt's outer regions.
S-types (stony) are made up of silicate materials and nickel-iron, and accounts for about 17 percent of known asteroids. They are brighter than C-type and they dominate the inner asteroid belt.
M-types (metallic) are made from nickel and iron and accounts for about 8 percent of known asteroids. They are brighter than C-type and they can be found in the asteroid belt’s middle region.