An asteroid is sometimes called a minor planet or planetoid. They are small Solar System bodies in orbit around the Sun. There are tens of thousands of them grouped in the main asteroid belt between Mars and Jupiter. They are smaller than planets but larger than meteoroids, meaning that an asteroid can range from a few meters wide to hundreds of km wide. The term ”asteroid” has historically been applied primarily to bodies in the inner Solar System since the outer Solar System was poorly known when the term came into common usage. In general, they are rocky bodies that do not have an atmosphere, although some have a high metallic content. A few have their own moons.