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. Depending on the impact of the asteroid it can cause craters up to ten miles wide. Asteroids can cause meteors to accrue. The way they form is that they get knocked out of their orbit and enter Earth's atmosphere and burn up.