They are made of hydron and helium. They make the front part of the asteroid belt. Other types of asteroids are the M-type, they are metallic. M-type make up the middle part of the asteroid belt. Another type of asteroid is the S-type, they are made of iron and metallic.
Most asteroids are only half the size of Earth's moon.
The two main belts are Garpra and the Ida. The asteroid belt slit the inner planets from the outer planets. Asteroids have known atmosphere. Asteroids can cause craters to accrue. The moons craters where formed by asteroids hitting the planets.