Why does Mars have a thin atmosphere?
Mars has a thin atmosphere because it lost its magnetosphere about 4 billion years ago. This allows the solar wind to strip air atoms away from it. See the Related Link below for more information.
Yes, because Mars has a very thin atmosphere. If it had a thicker atmosphere (similar to Earth), most of the meteors would burn up. Since it has a thin atmosphere, most meteors strike the surface. Also there is very little erosion on Mars, so when a meteor hits Mars, the craters lasts for a very long time.