Another difficulty that is unique to outer space is the presence of meteors and micrometeors. These are pieces of rock and metal that are left over from the formation of the solar system. Many of these objects travel at very high speeds. Under the Earth's blanket of air, people are usually protected from metor impacts. However, in space, people and spaceships are vulnerable to collisions with meteors. It is true that the chance of metor impacts is relatively small, but if even a small micrometeor happens to collide with a spacecraft, it could cause serious damage.