Moon and Mars 
The surface of Mars changes more slowly than the surface of Earth. There are no rainstorms or rivers to alter the Martian landscape, and no big “marsquakes.” And the Martian volcanoes appear to be dormant or even extinct. Most of the changes on Mars are driven by the wind.
But some changes come from outside Mars itself. Small space rocks hit the Martian surface by the thousands. These impacts gouge about 200 new craters per year that are as big as a pick-up truck or larger.
Planetary scientists arrived at that number by analyzing pictures from Mars Reconnaissance Orbiter. The scientists counted the number of new craters that have formed in one section of the planet since the craft arrived at Mars in 2006. They then used that number to estimate the total number of craters for the entire planet.
By comparison, Earth seldom gets any new impact craters because our atmosphere is more than a hundred times thicker than Mars’s. Almost all the space rocks that hit Earth burn up or explode long before they can reach the ground. The asteroid that exploded over Russia earlier this year was far larger than most of the space rocks that hit Mars, yet it left no crater — thanks to Earth’s protective blanket of air.
Mars is in view in the early morning sky right now. It looks like a moderately bright orange star in the east before sunrise. It’s especially easy to find tomorrow morning because it stands close to the upper left of the Moon.
Script by Damond Benningfield, Copyright 2013